I personally think Microsoft will buy Steam.
Unlikely to ever happen. Valve is a private company (IIRC) and Steam is its major cash cow right now.
Why else keep the GFWL client so under developed/resourced?
Lack of focus and resources. Microsoft seems to have put most of these resources into the XBox and XBox LIVE brands, leaving GFW with far fewer to work with. At least they seem to realize this mistake and are looking to correct it with Windows 8, but we've heard these kinds of promises before, but we'll see what happens as Win8 gets closer to release. If/when it hits MSDN I'm going to grab a copy and test it out.