I think that if Ballmer wants to buy “companies that are built around open-source products”, it is not so much as wanting to play fair with the FOSS community and products, but to be able to take out and fork products.
Let’s look at some scenarios:
a) m$ buys out a GPLed-product company. The developers get handsome payouts and assuming that these developers are true FOSS chaps, they could keep the code going as both GPL and m$ proprietary.
b) m$ buys out a GPLed-product company, keeps the developers and stop work on the GPL version. It then forks the code for it’s own purposes. The GPL version continues in the community and if it is of any use to anyone, will see a community form and thrive.
So, in two possible scenarios, the our friends in Redmond would have spent a tonne of money, made some open source developers wealthy (hopefully they are smart about asking for a lot) and the community still benefits because the code is GPLed.
Hence, it is not too bad that m$ spreads around the moolah they accumulated with thieving business practises and if nothing else, it would bring some good Karma to them in the end – sorta like how billg is now trying to do the “right thing” by spending money from the Foundation on medical research and related issues.
In the grand scheme of things, it can only point to good in how the ill-gotten gains of m$ can be made useful.