They launched Wave in May of 2009. It's not like they yanked it all that quickly.
Sometimes disrupting existing markets and paradigms takes time, patience, and several iterations.
(I'm still disappointed at how quickly they stopped the direct-sale idea with the Nexus One)
http://www.google.com/support/forum/p/android/thread?tid=6981e6d970e2f29f&hl=en