Carmen,
Let's not confuse video's with recordings. Now he may have recorded with his 4001 for Back to the Egg, but studio photographs I've seen show him playing his Yamaha and on his ill fated 79/80 tour he also played the Yamaha. As for "Off the Ground", I believe that photograph is at least 5 years old in that collage. Paul is good at using old pictures. On the "World Tonight" video it shows a still photo of him that was also used 11 years earlier in the "Press to Play" press kit.
I'm not sure why he doesn't play it as much. I quoted here on another thread what Paul said from the "Here, There and Everywhere" book in response to a question from a reporter on why he doesn't use his Rick. I'll have to look at his answer again.
I concede the ROCKESTRA theme. I have a picture of the entire gang at Abbey Road, and he does have his 4001 and I'll tell you this, it looked great in action with all those musicians. It's an awesome shot.
Anyway, someday he may turn back to it. Maybe when he's too old to stand with a bass and it won't be so hard for him to play sitting down with it.
