You can already:

<link rel="stylesheet" href="http://fonts.googleapis.com/css?family=Roboto:regular,medium...;

See this post:

https://plus.google.com/108761828584265913206/posts/JyBRu1gs...

Probably because they don't really want people to use it. I imagine the license has to be fairly open to allow for unencumbered distribution with android, but it's a part of the android brand. Every time it gets used outside of android makes it a little more generic and dilutes the android brand a little bit.

If it were visually distinguishable from Helvetica, maybe. But it's really not. It's more modern, more complete, and probably "better" in some typographical way that I don't understand. But it's really not. What this represents to the free software community is a repackaging of a Helvetica-like font in a way that doesn't suck. To anyone concerned about the "Android brand" it's a wash.

Droid Sans, however, is available in Google Web Fonts.