Can you point to a specific case? From what I can tell, the first two major cases were Nokia v. Apple and Apple v. HTC, in October 2009 and March 2010, respectively (and Nokia's not really part of the current kerfuffle of suits).
If you assert that Apple sued HTC because Nokia sued Apple first, that does not make any sense whatsoever. Nokia isn't even an Android OEM.
http://news.ycombinator.com/item?id=1166321
Over two years ago, I argued that patent suits were how the licensing game was played among the existing players. It was considered an everyday cost of doing business by the incumbents, but Apple wasn't well prepared for this. (They've learned fast.)
This wasn't on consumers' radar because none of the fights were as interesting as the juggernauts of Apple v. Android which get framed in almost religious terms and taken personally by users who have chosen a camp.
The argument then was that Apple had not been actively litgating patents, but when Nokia (faced with dwindling profits, most of which appeared to be landing in Apple's pockets) started the fight, and Kodak piled on, Apple had to demonstrate that the patents it was using to counter these suits were patents that it was actively defending.
This pushed Apple to file against HTC, and eventually against others who, again, had all been actively (but boringly) suing one another before Apple got to the table.