Mercurius
Legend
First, a key:
Hardcovers – pretty self-explanatory. A D&D book with a hard cover.
Softcovers – includes digest-sized books, non-digest soft covers, adventure sleeves and folders, etc.
Box sets – again, self-explanatory. However, I am not including the Dungeon Tile Master sets here but in accessories.
Accessories – non-book D&D items such as dungeon tiles, character record sheets, dice, DM’s screen, etc.
Other – Everything else that is vaguely D&D related. This includes miniatures, non-D&D games like Gamma World, board games, Heroscape, and one or two books that aren’t directly part of the rules (e.g. The Dummies book); it does not include novels or non-D&D related WotC products.
There are other ways to break this down but for the purposes of this discussion I think format is important. I also want to thank TerraDave, whose official D&D 4E products list proved very helpful.
Now some numbers:
2008
Hardcovers – 9
Softcovers - 6
Box sets – 1
Accessories – 5
Other - 3
2009
Hardcovers – 16
Softcovers - 5
Box sets – 0
Accessories – 6
Other - 5
2010
Hardcovers - 12
Softcovers - 10
Box Sets - 3
Accessories - 6
Other - 12
2011 (announced)
Hardcovers - 2
Softcovers - 0
Box Sets - 3
Accessories - 4
Other - 3
Let’s take a look at that in a chart form; for the sake of simplicity I’m going to combine hardcovers, softcovers, and box sets into one category, Books, because they are all of a general kind for the sake of this analysis: readable, D&D products:
Now given that there may be items in 2011 that haven’t been announced, especially in the 3rd and 4th quarters, lets look at 2010 and the first half of 2011 by quarter:
2010, Q1
Books - 5
Accessories – 2
Other – 3
2010, Q2
Books - 6
Accessories – 1
Other – 2
2010, Q3
Books - 10
Accessories – 1
Other – 2
2010, Q4
Books - 4
Accessories – 2
Other – 5
2011, Q1
Books - 0
Accessories – 3
Other – 2
2011, Q2
Books - 3
Accessories – 1
Other – 1
And here's the chart:
COMMENTS:
The big obvious sore thumb is the drop in the Books category in 2011. There was a huge spike in Q3 of 2010 due to the Essentials line, but then a plummet and an entirely book-less quarter to begin 2011. This includes a five month gap between the last book of 2010 (Monster Vault in mid-November) and the first book of 2011 (Heroes of Shadow in mid-April), as well as an eight month gap between the last non-Essentials book, and thus truly new material, in August (Psionic Power) and Heroes of Shadow.
The publication history shows that WotC has released an average of just over 20 books each year of 4E (62 total, including 16 in 2008, 21 in 2009, and 25 in 2010), with only 5 books announced for 2011. The Accessories and Other categories look to be more consistent, with miniatures replaced by board games and possibly other products. Now even if, say, a book is added in 2011 Q2 and maybe 2 in each of the last quarters, we're still looking at a huge drop in books to somewhere in the 5-12 range, or about half the out-put or less of each of the first three years.
Now I don't have the numbers but it is worth noting that even the 2008-10 numbers are down from the 3.5 days, which saw 30-40 or more books published each year; if you go back to the 80s and 90s, it is many more again. Even if D&D Insider can make-up for some of the lost book content, I think it is undeniable that Dungeons & Dragons is in noticeable decline.
Finally, it would be interesting to follow up with at least two further studies: One, breaking the same info down by type of content rather than format (e.g. core rules, expansions, settings, themes, adventures, etc); two, comparing all of this data with earlier editions. Maybe when I have the time...
Hardcovers – pretty self-explanatory. A D&D book with a hard cover.
Softcovers – includes digest-sized books, non-digest soft covers, adventure sleeves and folders, etc.
Box sets – again, self-explanatory. However, I am not including the Dungeon Tile Master sets here but in accessories.
Accessories – non-book D&D items such as dungeon tiles, character record sheets, dice, DM’s screen, etc.
Other – Everything else that is vaguely D&D related. This includes miniatures, non-D&D games like Gamma World, board games, Heroscape, and one or two books that aren’t directly part of the rules (e.g. The Dummies book); it does not include novels or non-D&D related WotC products.
There are other ways to break this down but for the purposes of this discussion I think format is important. I also want to thank TerraDave, whose official D&D 4E products list proved very helpful.
Now some numbers:
2008
Hardcovers – 9
Softcovers - 6
Box sets – 1
Accessories – 5
Other - 3
2009
Hardcovers – 16
Softcovers - 5
Box sets – 0
Accessories – 6
Other - 5
2010
Hardcovers - 12
Softcovers - 10
Box Sets - 3
Accessories - 6
Other - 12
2011 (announced)
Hardcovers - 2
Softcovers - 0
Box Sets - 3
Accessories - 4
Other - 3
Let’s take a look at that in a chart form; for the sake of simplicity I’m going to combine hardcovers, softcovers, and box sets into one category, Books, because they are all of a general kind for the sake of this analysis: readable, D&D products:

Now given that there may be items in 2011 that haven’t been announced, especially in the 3rd and 4th quarters, lets look at 2010 and the first half of 2011 by quarter:
2010, Q1
Books - 5
Accessories – 2
Other – 3
2010, Q2
Books - 6
Accessories – 1
Other – 2
2010, Q3
Books - 10
Accessories – 1
Other – 2
2010, Q4
Books - 4
Accessories – 2
Other – 5
2011, Q1
Books - 0
Accessories – 3
Other – 2
2011, Q2
Books - 3
Accessories – 1
Other – 1
And here's the chart:

COMMENTS:
The big obvious sore thumb is the drop in the Books category in 2011. There was a huge spike in Q3 of 2010 due to the Essentials line, but then a plummet and an entirely book-less quarter to begin 2011. This includes a five month gap between the last book of 2010 (Monster Vault in mid-November) and the first book of 2011 (Heroes of Shadow in mid-April), as well as an eight month gap between the last non-Essentials book, and thus truly new material, in August (Psionic Power) and Heroes of Shadow.
The publication history shows that WotC has released an average of just over 20 books each year of 4E (62 total, including 16 in 2008, 21 in 2009, and 25 in 2010), with only 5 books announced for 2011. The Accessories and Other categories look to be more consistent, with miniatures replaced by board games and possibly other products. Now even if, say, a book is added in 2011 Q2 and maybe 2 in each of the last quarters, we're still looking at a huge drop in books to somewhere in the 5-12 range, or about half the out-put or less of each of the first three years.
Now I don't have the numbers but it is worth noting that even the 2008-10 numbers are down from the 3.5 days, which saw 30-40 or more books published each year; if you go back to the 80s and 90s, it is many more again. Even if D&D Insider can make-up for some of the lost book content, I think it is undeniable that Dungeons & Dragons is in noticeable decline.
Finally, it would be interesting to follow up with at least two further studies: One, breaking the same info down by type of content rather than format (e.g. core rules, expansions, settings, themes, adventures, etc); two, comparing all of this data with earlier editions. Maybe when I have the time...