Certainly is possible. Last year, Apple intro'd 2.0 simultaneously with the 3G. It's possible that Apple wants to avoid introducing new hardware and software this time around - especially given all of the problems associated with last year's MobileMe launch.
Why not release it before the new hardware? That way you get people all hooked on it and then bring out a new hardware and say, "If you like what 3.0 does on 3G, look what it can do on THIS!" or something to that effect.