I don't think this is the case at all. AD&D came out in 1977, and 2nd edition was released in 89. Both systems were very similar; unlike the jump from 2e to 3e or 3e to 4e. It was easy to switch from a 1e campaign to a 2e campaign. This represents a 22 year period, with little growth in the core mechancis; but it continued to be popular till the late 90s; and much of its decline has as much to do with poor book keeping and management more than stagnation. I do think 3e was a needed change; but I had hoped to see a similar period of stability. The problem with Changing from 3.0 to 3.5 in five years, and then changing over completely to 4E just a few years later, is it is too much growth and change. The biggest problem with 3E wasn't a lack of growth, it was the number of really bad books Wizards was releasing and rehashing to support it. The last string of Splat material was so over run with typos, ommissions and meaningless advice, the only reason to by them was to break the system. If anything, 3E needed to be more moderate in its development; and supply gamers with supplements that added to the game, but didn't break it mechanically.
There is something to be said for having a steady system that everyone knows the rules for, and it isn't stagnation, its stability. This helps the hobby grow. Releasing new editions every few years, fragments the community, as we have seen with the release of 4E. I am not saying 4E should never been released. But for me, it was way too soon. I had just finished updating my splat books to 3.5, and then they announced a new edition; an edition which required purchasing a new PHB each year to stay current with. Had it come out in 5-10 years, I would have been much more open-minded to the idea. But I would be lying, if I said a little resentment didn't creep into my evaluation of the new edition.