I believe it. While I don't exactly have ADD, I do find it EXTREMELY hard to focus on things for a sustained time, and I've been playing games most of my life.
I guess it could also just be that I'm getting older, but I tend to not have any problem focusing when I play games.
Sounds exactly like me. I never really noticed it until I was into my 30s. But I've gotten really bad at focusing on any one thing at a time. When I play games (and I tend toward RPGs, and HL-type shooters mostly), I don't seem to have much trouble concentrating on them.
"The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts." -- Bertrand Russell (I think...)