You’re making a mistake that many are making: that the lawsuit is about the validity of the patents. It’s not. It’s about whether or not HTC violated patents that Apple was legally granted. On the surface HTC appears to have done so.

HTC, Microsoft, or Google could chose to separately challenge the validity of the patents. However, there’s a good reason they might not. Doing so could put their “vague and generic” patents under scrunity.

The real problem here is the current patent and copyright system.

So why HTC?

Well, when you hit someone with a nuisance suit you want a target small enough without the financial resources or patience to put up with a potentially long and costly litigation but large enough that any concessions gained to be consider significant precedents in future court proceedings. In Apple’s eyes, HTC fit the profile.

So what about Google and Microsoft?

Obviously Apple felt that Google and Microsoft were to big to go after directly and felt that HTC was a weakness. I believe at some level Google and Microsoft see the Apple suit as a threat and have probably adopted a wait-and-see strategy. If the case goes badly for HTC, Google and Microsoft could petition the court to join the case in some matter and make their considerable resources available to HTC. Obviously neither Google or Apple want HTC to make any concessions to Apple or a court decision favorable to Apple.

Of course, what Apple is doing is playing the game. Given that the U.S. Patent office will grant a patent to any wacky idea scrawled on the back of a used Kleenex, copyright law has been so screwed up to accommodate a certain mouse in Florida, and there’s absolute no financial consequence for losing a nuisance suit, who cam blame Apple for pursuing a strategy that at the surface appears to be in long term interests of its shareholders.