I think 10% is perfectly fair for that kind of service. The argument about them handling the searching around for you, instead of doing it yourself can be said for just about any business venture. It's a convenience fee.
We tip delivery people 20+% because we don't want to drive to the restaurant ourselves.
We pay $2.00 every time we go to an ATM to take out $20.00 so we don't have to go to the bank.
If you don't want that convenience, you don't need to pay for it. I personally don't have the time or energy to shop around and email dozens of sites, so I'd PREFER to pay the 10% just so I don't have to do any of the work selling it.
Really, like they said, 10% to act as an agent is incredibly cheap. Look at the commissions people in other businesses get.
You can technically purchase a home without a Real Estate agent, and you can represent yourself in court by researching the laws/consequences in your area (instead of getting a laywer) if you really want too and if you don't like the fees those people impose on you.
It's just another convenience fee, and really if you don't want that convenience, you don't need to use it.
Shopping around costs you 0%.
I don't think they deserve 10% if you make a deal on your own, however.. but if they find you a buyer, or a buyer finds you through a service they've created, 10% is perfectly fair.
Let's assume Luis 40/40/20 split on a $4000.00 game.
$400 taken off the top.
Programmer: $1440.00 (As opposed to $1600)
Artist: $1440.00 (As opposed to $1600)
Audio: $720.00 (As opposed to $800)
Scaling up/down shouldn't be a problem, since we're dealing with percentages.
And really, the numbers are still pretty nice if they can handle all the grunt work of getting that game sponsored for you.
Don't think it's fair? Don't use it.
I'll bet in the years to come, as Flash games become even more advanced, and make even more money, that percentage will creep up to 20%-30% and it wouldn't surprise me if some portals decided to only deal with brokers, to limit work they needed to do to find solid games.