Microsoft didn't have anyone serving on the board at Apple, nor were they invited to be a deep part of the iPhone like Google was. Apple targeting Android with patent lawsuits seems to be mostly driven by the sense of betrayal Jobs had for Google/Schmidt, and his opinion that Android has stolen much from Apple.

Most of the other lawsuits Apple have been involved with are more defensive in nature. Nokia, Motorola, RIM, and Kodak filed against Apple first. Apple has been the plaintiff in the Samsung and HTC cases.