The Galaxy Nexus is stock Android. Apple is suing Samsung because of stock Android software - not firmware, not hardware, but software. Is there a legal reason Apple is suing Samsung instead of Google, or is it tactical / political?
Because Samsung is shipping a device with the software. Parent law does require that the patent be tied to a physical device. IANAL.
That's why you can build an mp3 player from source without paying the license fee, but Debian can't ship you a compiled mp3 player.