This one is long over due. When Visual Studio 2005 was in beta there was a alot of contraversy that the test tools would only be included in the team suite. Many organizations are not willing to purchase the team suite, either due to cost or they simply don't need the tools. As a result we still have many organizations that do not utilize unit testing and those that do are probably using NUnit or something similar. Somehow the message has gotten through to redmond and Orcas will finally deliver unit test tools that don't require the purchase of the team suite.
You can check out the details in Naysawn Naderi's blog