Yes and no. While x64 has existed as long as you say, 'proper' Windows support didn't start to appear until maybe a year into the Vista cycle. Driver support on XP x64 never materialized and the early Vista drivers were extremely problematic.
So I'd say that "usable" Win x64 is probably about four to five years old.
I do agree that pretty much everyone should be migrating up to x64 by now, though.