I'm very surprised there is no package manager in use too, apt (advanced packaging tool) seems to be the thing that impresses users new to ubuntu most, although the cut down version of dpkg (what apt is based on), ipkg, never worked well for me.
Could be google are trying to leave every aspect of the OS as open as possible to see what the users decide is best for them, it should be fairly simple to port dpkg, rpm or even portage (the more popular package managers on linux) to android or use a (heavens forbid) install shield type system. Depends on whether users want a central software repository for everything or are happier finding apps all over the net and installing them. Heaven help us if they choose the second as android will probably go down in history as the most insecure OS ever.
As for apps getting broken between v1 and v2, tough shit, it's in development and such an early release (even if its version 1) should be regarded as a beta and should remain a beta until users have been at it long enough to break practically everything. I have been advising everyone I know to wait another 6 months if they want to do more than just try it.
Nearly forgot about the fragmentation comment. An upgrade from version 2 to version 2.1 is fragmentation? WTF? Should the lusers go back to windows version 1 as everything else is fragmentation?