Crunch will sell books that fluff cannot. People LOVE options of things to play. Setting crap is something only one player needs... the DM. And he can make up his own. Crunch is useful to 100% of players. So Crunch is what needs to be on store shelves.
There's other points as well. But this one is the most important... that removing crunch from physical sales will lead to the death of the game. I figured that'd be the most important.
I think that's the way it's BEEN, but I'd be interested to see how it actually IS now. Do the crunch books outsell the DDI? Unfortunately I doubt WoTC is going to give us any numbers.
I can say for myself I pretty much didn't buy the crunch heavy splat books. The 4e books I've bought have been the more flavorful ones- the ones I enjoy sitting around reading and getting inspired. The crunch I prefer sitting in my CB for when I need it. I realize that's how I like it, but I wonder how many of me there are out there.
This was kind of true in 3e as well for me. I said in another thread that I bought pretty much all 3pp stuff, and that was mainly because the flavor was much better. (I was a huge Scarred Lands fan.) Half the time it even ended up causing me to overlook the crunch. For instance I tended to get annoyed at the Malhavoc Press stuff crunchwise, but loved the flavor, so I ended up buying/using a lot of his books.
As far as the rules only in the DDI...
A while back I sold all my DVDs. I didn't buy blueray, nor will I. If I want to see a movie I stream it either from netflix, or Zune.
Yep- I don't own anything anymore, and I'm just renting stuff... But: It's just not worth lugging all that crap around, and since it will inevitably be replaced with some other format anyway (Who still watches their VHS tapes? and now I know someone will say they do just to prove someone wrong on the internet.) what's the benefit of buying it? (I guess I can pull them out and show them to my grand kids so they can laugh at how crappy everything looks...)
Now I don't know if I can say the same thing about the DDI... With movies and music, despite the format changes the content is still the same... So if say a new way to stream comes out that is higher quality, I know I'll still have the same movie... Dunno if DDI will always hold 4e.
If WoTC started adding all of their game catalog to the DDI, and indicated that in the event of a new edition 4e would still be in the DDI... Then I'd be tempted to be fine with an all digital thing. I'd probably want the tools anyway when I was playing the game.