The difference is that Apple's update is mostly under-the-hood, while the Nexus One gets support for multitouch. The pinch and stretch, two finger goodness was previously only available on the iPhone (in the U.S.).
As reported by Engadget:
they've capitulated and enabled multitouch in Browser, Gallery, and Maps -- great news and a big win for the Android community at large.
I still can't get the update on my Nexus One, it claims "your system is up to date." I'll update this post with more details when I get them.
Any N1 users want to chime in? Get it yet?