Web Apps are a very real part of the future of the web. The fact that this space exists in the first place whereby there was only desktop apps previously should be testament enough to that. I may not personally agree with Mozilla in regards to the role of web apps, but I think that we all agree, it's better to be in a position to allow users to make their own minds up rather than go off of what a few loud naysayers want.
If Wev Apps are a very real part of the future of the web why isn't there a standard for that? Or in another words, if it is the future why haven't they all sat down and agreed upon a standard??
This way we'll be begging jQuery for Web Apps or some other abstraction layer that will do all the dirty work of cross browser compatibility...
Most of Web Apps are already in the standard (appcache, indexeddb, etc.) and I know there has been some communication around manifest formats (but I'm not directly involved in that).
Generally speaking, though, the difference between one definition of "web app" and another is very small, in terms of what the platform has to support.
I'll also note the perspective that sometimes it takes a couple of implementations before the "right" solution is known. Many evolutions of the web standards have followed varying implementations being played with in the field.