Nice one, - and thanks for the link.
I suppose that at some point, there has to be a judgment call as to which social network sites are included in the list for selection, otherwise you would have approximately 334 icons to try to fit into the list, and 334 bits of code programmed to be added to your page if selected. I'm not sure how that would reflect on the cost of the extension, though.
I don't deny that MySpace is still a top player in the US where it is still the largest 'social network' unit (although I feel compelled to add single quotes to 'social network' in their case) but I really can't see it being around for too much longer, at least under the guise of being a 'social networking' site. News Corp is desperately trying to off-load it (no one will touch it) despite a few re-builds to try to breathe new life in to it. In Europe and the rest of the non-US world it is dying a slow and pitiful death. It may continue as a resource for musicians' band/fan pages (especially if a buyer were to rebuild/rebrand it specifically for that purpose), i.e. - for bands like The Chemical Brothers who don't actually have their own website, but I personally find the pages currently to be tedious, messy and aesthetically repellant*.
For people who want access to all possible options, there is always Add This. But I expect WA might add MySpace if enough people ask for it.
* An entirely subjective personal opinion, possibly shared only by the most marginal minority of the grossly bigoted and opinionated.