Imaro
Legend
You're kidding, right? WotC made more money selling the respective "core books" of 3E, 3.5E and 4E than they did of anything they published after it. The one thing that has been shown is that people WILL buy a new edition's first set of books. Always. Much moreso than anything they might publish in Year 8 of this decade plan you mention. And the reason why is that it's a "new game"... and new games usually get bought in greater numbers that supplements to existing games.
You do realize the decade claim was made by WotC themselves right? It's in the 4e PHB where they make the claim that 4e would firmly establish D&D for the next decade. Of course now that we're at the end of the road we know that 4e didn't last anywhere near a decade... I guess my point is that I don't think it's unfair to call them out on the fact that maybe they shouldn't have established that as a benchmark for the last edition.