Also, if these developers really wanted to, they could distribute it directly from their site and dynamically generate the extension, packaged with a unique identifier, for each download. This would make it effectively unblockable. So simply identifying an install of this specific extension is not a solution.
Actually, Google does track all of this stuff already:
http://adage.com/article/digital/inside-google-s-secret-war-...
Google could decide to just ignore IPs that host users that display this behavior pattern. But yeah, it's "easier" to just ban the offending Chrome extension.