Actually people do leave, if you notice after the MK9 GF the viewer count dropped for a bit. Same with after MvC3 GF.
And even if you say is true, it is no coincidence that during pool stream on friday, MK9 got 8k~ and SSF4 was sitting at 25k. The whole day was dedicated to those two games, so if you tuned in to a particular stream it was because you wanted to watch that particular game. Not because you were waiting for something to come up afterward.
And notice how the ratio for MK is massively and utterly worse than it was in the original ratios quoted that I contradicted. So your ratios alone prove the 56-57k is a vastly inflated number that had jack all to do with MK. Because when it was one stream and not take your pick, MK did far worse ratio wise.
Hence, that large stream number speaks vastly more about EVO than it does any individual game, so take it with a large grain of salt.
EDIT- if you watch WCG or any sort of PC gaming event this also holds true. Finals eclipse everything but it's mroe about the event. Even though the RTS and FPS crowd couldn't give a rats ass, they do tune in.
I'd say MK's registration numbers, and more importantly individual registrants mean a ton more, and the showing seemed to be pretty good.