It really could, and it really needs to. The default looks is a pretty sure way of ensuring that people who are browsing for an alternative to the Mac aren't going to pick Ubuntu.

It's a matter of personal taste, but does anyone honestly look at the default Ubuntu desktop and think "Well, that's just the pretties desktop I've ever seen".

Logically it shouldn't matter, the look has little influence on the functionality, but I really think the orange, black, and purple look has turned people away from, if not Linux, then certainly from Ubuntu.