Regardless of how patent-heavy mobile devices may be, this represents a major change in Apple's policy.

In some discussion thread in the distant past, someone pointed out that Apple has never used its patents offensively. And a quick check through Wikipedia seems to confirm it: The only mention of patents was in cases where Apple had first been sued for violating a competitor's patents.

http://en.wikipedia.org/wiki/Apple_Inc._litigation

Up until now -- well into their reign in the mobile device sector -- Apple could claim that they were only amassing patents as a means of defending themselves from other companies with patents. Hence, this preemptive strike is unusual.