This rings true to my ears: prior to suing HTC Apple engaged in closed-doors talks with tier-1 (top-level) handset mankers warning them of coming changes in their own iPhone-IP defense strategy. Those "warning shots are meaningfully disrupting the development roadmaps for would-be iPhone killers;" while the lawsuit against HTC appears to be Apple's way of underlining the seriousness of their action, "a public exclamation point" for the process.

Read on for ObLitGoogRef. below.

"Apple talks tough to handset makers" by Philip Elmer-DeWitt

"[...] Why pick on HTC? [Report author] Reiner speculates that as the earliest and most aggressive user of Android, HTC was the perfect proxy for Apple's real target: Google (GOOG). It helped that Apple and HTC didn't have any supplier relationships that could be disrupted by a protracted legal battle. [...]"
http://brainstormtech.blogs.fortune.cnn.com/2010/03/09/apple-talks-tough-to-handset-makers/