why not using google sites so far

Hmmm ... let's see how they promote it - quote from their help: You can search across Google Sites pages and content using powerful Google search technology. You'll find specific pages and documents instantly, the same way you would on Google.com.

While free/open is good and competition with Microsoft Sharepoint is starting - I really doubt anyone would love to see on google their internal product they are working on ... :-)

Maybe if the product is fully instalable inside a company's intranet - that would change any fear of leaks.