Not sure about the bashfulness bit but if it's there it's probably not too different from a person looking at an old photo and thinking, jeez I had that hair and those clothes?!
Yeah, there may be a cultural element of being self-deprecating too. Didn't Phil say he'd have left Genesis in a heartbeat if Led Zeppelin (or something) had asked him to join? I may be misremembering and it's somewhat tangential to the topic at hand. I also remember him comparing Genesis to another big band - I think it was U2 - and saying that they (Genesis) just didn't have that confidence. He said something along the lines of "man, if we were just a little bit better we'd be great!". He was making a wisecrack I guess, and it's certainly not specifically casting their older material in any kind of negative light, but they do from time to time seem a little chastened by all the the flack they came in for over the years. Which was totally unjustified in my eyes! And maybe it's just Phil.
I read an interview in which Banks spoke with obvious pride about Supper's Ready and Duchess as two of the best things they ever did.
Rightfully so.