If you haven't read this article I recommend skimming it, it provides an interesting opinion on the various VS SKUs: http://www.developer.com/net/net/article.php/3577266
Here's an interesting comment on the VSTA SKU :
"Now, if you have to choose a Visual Studio Team edition, then you most likely want Visual Studio Team Edition for Software Developers. This version has all the core language features and unit testing. Full-time testers may want the edition for testers and full-time architects may want the Architect edition. (However, almost no one should be happy about Studio for Architects because it doesn't include testing tools. So it's okay for architects to design and code some of their designs, but not to unit test them? That's dumb.)"
Mark Groves, a Sr. Program Manager, really says it best below:
"I cannot say I disagree with the article, but I will also say that I don’t think the audience the writer is targeting is our target audience. Shops that currently run VS Professional with VSS for example, may not be our target market. Larger orgs, that currently have Rational Tools, for example, is easier market for us to break into. In my opinion, the breath of the offering is what sells large IT. It is much easier for a CIO to agree to a purchase from one vender then several combined. This is why having, as many integration points between the tools is important. My last org spent over a million dollars on Rational products, that was a CEO level decision. As you can imagine our CEO did not care about the details of the tools, he was interested in the breath of the tools, and that they covered areas of concern for his org. "