Hell, while I'm at it, I've got an expanded question to follow up my last one:
Why would anyone developing a web application today sink any money whatsoever into a platform with any degree of proprietary technology?
The latest Scoble dispatch is asking about Microsoft, but what about all the other closed-world web development environments out there? Really, it's been awhile since I've heard much about anything other than Microsoft versus Open Source in the web development world. And, when I have heard about the other guys, it's usually in a scenario where someone got roped into the technology sometime in the dot-com boom days and have since built everything around it.
It seems this far out from the initial adoption that decisions are made less and less from technical merit, and more from monetary and political merit driven by the sales force. The momentum of the platform maintains lock-in, despite any resulting impedance mismatches or inefficiencies which may crop up as the platform matures or (less charitably) ages.
Finally, consider one of the main routes for finding support for Open Source platforms: Google. Have you run into a cryptic error message? Google it. Need to find docs for an API? Google it. So many of these wholly proprietary platforms have locked up a lot of their docs and forums behind for-pay password walls that Google never sees.
Now, for now at least, it seems Microsoft has avoided these things. But, my suspicion is that they're only able to do this as a commercial venture because of the sheer number of people and the wads of cash they have. Eventually, I expect even they will be overrun. I couldn't imagine a new closed-world web development platform taking off today.