Sound familiar? Of course it does. HTC acquired S3's patents, which can be used as ammunition to fend off Apple's various lawsuits. The International Trade Commission already ruled that Apple is infringing on two S3 patents.
These are wild times in the patent landscape. A company like HTC can spend $375 million acquiring patents (S3 and ADC combined) and justify the returns based on lawsuit defenses. On the surface, HTC's latest patent lawsuit looks run of the mill. But judging from the patent acquisitions of late you can assume there will be many more lawsuits on deck.