As for U2 retiring...
I'm not sure U2 ever "created culture". I'm not even sure what that means. I know of no ordinary people who saw U2 and suddenly dressed like they did or acted like they did. In contrast, this was true for artists like Madonna. U2 revived the political scene in the 80's and that may have seemed "fresh", but that's only because other bands did not focus on this area. However, as we all know, that was hardly new. ZOO TV was indeed great, but again Bowie and Pink Floyd had done similar things in the 90's. So again, where's the "creating culture" part?
Based on the success of the last album and tour, it seems TONS of fans are more than happy that U2 are still around. Given the success of the current album and the sold out tour, it seems these same fans - and more - are more than happy U2 are still around. And given that U2 can create a "Mofo" followed by a "Beautiful Day" and then a "Love and Peace or Else", I'd contend that U2's creativity is still high.
Lastly, given that U2 empowered the legal download world, becoming the first artist to truly advertise their work this way (and one of the reasons Billboard changed their charts to include downloads), I'd say U2 are "creating culture" more now than ever.