Help me out here... (we can keep this brief...)

The 57% is the CAP and is calculated after the owners get $1 billion off the top first.

$8 billion total revenue - $1 billion off the top = $7 billion

$7billion * 57% = $3.99 billion

That's the CAP, but the entire cap is not always spent.

To figure out the 2010 cap you would need to know the 2009 total revenue, though.

Excellent! That's the info I was looking for!

So now let's do a little calculation for others who are wondering also...

(NFL proposed 2011)
$9 billion total revenue - $2 billion off the top = $7 billion

$7billion * 57% = $3.99 billion

(If it stayed the same as it is...)
$9 billion total revenue - $1 billion off the top = $8 billion

$8billion * 57% = $4.5 billion

So, what the NFL is proposing ends up being half a billion less than what the player's share would be if they left it where it is. I think this is the rub. Sure, the players aren't taking a "pay cut", but they're not getting what was mutually agreeable to both parties at the last negotiations.
I can see the argument now.

Let me try to sum this up...

Players:
"We're partners in this endeavor. You get your initial cut, then we get this percentage after that is taken out. This way, as the popularity of this business grows, so does both of our revenue streams."

Owners:
"We're partners in this endeavor. We require more of an initial cut since costs have risen. You (our partners) will make the same $$ you were making, and we'll keep the extra ten-plus percent in revenue. (1 billion dollars)

Players:
"Oh, we think not."

and the battle began.