[Mike Haven]

interesting question

i would guess it's from a combination of old timer pros' stated earnings, sims, and mathematical likelihood

don't forget that poker is a nil win/loss game if all players play as they should, so to get above the line you need someone else to play badly enough to remain below the line, constantly - it is perhaps unlikely that other players will constantly be incredibly below the line in any particular game so that you can sustain much more than a few bb's per 100 - although, because of the sudden increase in numbers of players, with good game selection the old school's figures may prove to be too low for a while, until the new players either bust out or get better