Microsoft has a smart marketing strategy compared to other mature technology companies. They have made it very obvious during the OS2 vs Windows battle many years ago and continue to do it with their cloud computing strategy.
Apple on the other hand has an excellent product (user interface that is way ahead of others) but they need to keep coming up with innovative products as their products usually get copied in a few years e.g. Droid in smartphone and Windows 7 in desktop OS.
Google is a world by itself that keeps growing without a huge sales force that other companies are saddled with. They build products that sell themselves using open source and standards.

I am currently using Google for mail, etc with a MacBook Pro and they blend together like a delicious smoothie!

Other potential IBM acquisitions are SOASTA - a cloud computing testing specialist and Service-now, an on-demand IT service management firm. And while there are spending $15B, what about RightScale and Sonoa?