Varience in poker is much greater than the majority of people give it credit for. Yes downswings happen to winning players and they are often contributed to by bad play but occasionally not.
I have seen an example of a big winner in mid/high stakes cash game online (cts i think) breaking even over 100k hands. Recently sng grinder spacegravy completed a challenge to make 25k in a month from $60 games. He did it averaging an ROI of around 7-8% but in the middle of it broke even for 2000 games (wow).
I think you should have specified "online" in your first paragraph, poker didnt get invented 3-4 years ago with the inception of online poker, people made a living playing ONE table live for 20 years previous to that, how significant a factor is the varience playing live 7 card stud for a living on one table where every hand takes 10 mins to play and you have to utilise your ability to play marginal hands and situsations in comparison to playing 12 tables nlh online? hendon mob, tony bolton, a lot of u.k players that would turn up for a cash game with 50% of their roll in their pocket and substute a profitable income thus for a full time job/career elswere without giving a consideration to ROI, EV ect, just playing hand for hand poker and making player dependent reads, the nucleus of live cash game poker, I dont think that variance is an applicaple concept indepent of online poker, it doesnt really matter, it just makes me laugh at all the internet bods that think poker was a game invented 4 years ago and developed by university students that supplemented there student fees by playing poker inbetween playing dungeons and dragons or whatever the fuck it is computer bods play and eating pot noodles.
Anyway, how the fuck can you be on a 2 month "downswing" at those levels?