This strategy is perhaps the biggest mistake. Bands can change their style over the years but good bands, while evolving, keep their roots--you don't see most artists changing from Rock and Roll to Polka or from Classical to Hip-Hop. There is no real reason for D&D for keep changing the rules so much each decade. Hasbro doesn't constantly change their best-selling boardgames, AFAIK Magic: The Gathering still has the standard rules.
Hi, hope you don't look down on me for being a first-time poster here, but reading this...makes me want to recommend you go read some of the designer's articles on Wizards.com regarding Magic. Because at least a few years ago, Mark Rosewater was writing on how and why he broke the rules of the Gathering. All the time. (kinda took a break from card games so haven't read it recently...) I'm not sure if he ever said it, but I will say that breaking the rules is pretty much a part of every set.
Here's some example articles, I'm sure there's others, some may even be more recent:
Gimme a Break : Daily MTG : Magic: The Gathering
Rules of the Game : Daily MTG : Magic: The Gathering
ah, here's one:
-1/-1 Singular Sensation : Daily MTG : Magic: The Gathering
Now none of that may be meaningful for D&D, but I do think an understanding of some of the philosophy in other parts of the company may help alleviate some of your fears. They aren't just sitting on Magic and putting out new cards with different names and pictures, but are expanding their horizons, pushing the limits, and otherwise improving the game.
As far as their boardgames go, well, I have Transformers Risk. I like it. It does change some rules, and does offer some variety. I know I wouldn't be happy if all I got was some different risk pieces or a map, without any real meat to it. Probably why I'm never tempted by any of those themed Monopoly's. Either that, or I just have no desire to buy any college football stadiums.
Unless there is a common tie between editions, continuing to change the game radically every decade will diminish D&D being a common bond between gamers. The Old School 3e / 4e battles will continue and get worse--the player base will fractionize more as more reboots occur, and I believe D&D will begin to lose its identity as the more common question will be "what edition do you play".
That hasn't been a problem since the 80s? There have been lots of changes over the years.
Yet at its core, there's still this thing we call D&D.
I'm not particularly afraid of waking up one day and finding out that I'm playing something I can't recognize. Maybe that'll happen one day in the distant future, as the core of the game disappears. Maybe that should be prevented. But I do respect the need for some changes, for some growth, and yes, I do realize that can occur at some level of the rules. Some of those changes I'm glad to see too. I really do appreciate the elimination of those thief skill tables, for example, and those silly rules about monks having to defeat other guys to level, and those race/class limitations...
I don't know 3rd edition that well, but when I look at the evolution of the game over the years, I keep thinking that it's getting better all of the time.
PS, I'm really glad Elvis didn't stay a gospel singer his whole career.