I suspect that one day in the near/distant future we'll all be using a controller and a laptop, period. I already do that for some of my production work using Reason, and when I perform on a grand piano I just take my laptop for SMF playback.

However there is something to be said for playing an "instrument" - a keyboard with it's own unique sounds. I don't think that's going away anytime soon. Having just bought a Motif ES 8, I really feel like I'm playing a very advanced instrument with a terrific keyboard that is made especially to provide full control over the Motif's many sounds and functions. I doubt if a separate non-Yamaha controller could improve upon that. You'll always find that the buttons and controls of Brand X MIDI controllers never really match up to the functions of Brand Y module in the same way that a dedicated keyboard does.