I think that also would depend on the game type, or to whats in at the time and how heavy they advertiser. I remember when I did Phoenix Racing, probably the worst game I ever programed back on the a6 (gotta love a development lead who likes to feature creep), but the game hit over 2 million downloads in 6 months, but Grand Auto was just coming in, and the guy they had promoting it spent every day putting it on every free download, and talking about it in every forum he could....
Where Office Purks, I sold it to two publishers and did nothing to promote it, and the game only sold like 2800 units....
Dont know if that helps ya or not