They already do. Its called Postini, and some of the biggest corporations in the US already use it.
It's no surprise that they concentrate on marketing their business software to businesses though. That's who's going to pay for it. A CS department is going to use whatever the school uses and a non-profit is better served by Google Apps (which is discounted heavily for non-profits).
Also, 80beans is using it and they only have a team of 6.