Technically the Chromecast is running a heavily modified version of the Android OS with a lot of key components stripped out. Realistically, it probably isn't going to be running a full-fledged Android release with app support anytime soon (or at all).
While I agree a RaspberryPi unit running Raspbmc can do more it isn't going to do it for $35 and it isn't going to 1) play Netflix or 2) easily stream any desktop content you want.
The basic board for the Pi is $35, a cheap case is, at minimum, $10, you'll need an SD card (another $10 or so), an HDMI cable ($3), and as far as a remote control goes you can either use your phone (free or a few bucks) or buy a remote with dongle for around $20. So realistically you're already about $60 into the project without Netflix which is a big deal breaker for many people.
I love the Raspberry Pi and XBMC, in fact I'm the one responsible for writing the majority of Raspberry Pi and XBMC articles on How-To Geek, but for $35 the sheer ease of use and instant Netflix access provided by the Chromecast is a really great value. I wish Raspbmc (or Linux in general) would get native Silverlight support so I could watch Netflix in Raspbmc, but that's not happening anytime in the near future (and because of various DRM issues it probably won't ever happen). Right now the only option for a Linux-based XBMC install to get access to Netflix is to use some sort of Rube Goldberg like in-home streaming server setup to sling the Netflix from a system that supports it (like a Windows 7 desktop) to the system that doesn't (the raspbmc unit).