no one was looking for wave
And people aren't looking for a replacement for email, or instant messaging, or blogs, or wikis. Those tools all work great for their intended purposes, and whatever technology augments them will likely offer a different combination of persistence and immediacy than those systems. Right now, Wave evokes all of them without being its own distinctive thing. Which means it's most useful in providing reference implementations of particular new features.
Never mind the "Pushbutton platform" stuff that comes in the paragraph after, it's this paragraph that matters. No one was looking for Wave.
Regardless, kudos to Google for killing it so quickly. No matter how obvious it is that it needs to happen, killing children is never easy.