Yeah, I would say it's probably pretty common, but also I do think a lot of bands that do try to do new big things are actually pretty successful at it reinventing their sound. Even with Paul McCartney's distinct voice, the early Beatles and late Beatles are completely different experiences. Look at the Rolling Stones...it's always Mick Jagger, but I only like less than a decade of the Stones (which I absolutely love), and the rest I could completely do without. It's not like they sucked...other people love these distinctly different eras of the Stones. Early Radiohead vs. late. Daft Punk.
Pearl Jam is always going to sound like Pearl Jam. Same with Weezer. But I do think the uber talented who don't have those overwhelmingly recognizable voices can do a lot to become something totally new-sounding.
Also, I think a lot of the time it's a personal thing. It doesn't happen to me with Leo, but I can see that if somebody were to say that's how they view him.