100K in a day seems like sloppy astroturfing. Why not add on smoothly over the course of weeks? At only $800/thousand followers, perhaps $80K was spent by an Obama supporter to create a news story and discredit Romney? Perhaps Romney was the inadvertent target of these astroturfing firms' efforts to make their fake users seem more legit? I checked out Obama's follower stats, and he experienced no such bump. Why pick sides if your goal is simply to sell fake followers random folks?
[I'm not necessarily a fan of either major party candidate, so please don't consider this a political discussion.]