Exactly. And you're not just dealing with the portal but also all their affiliates, which means by the time the deal is done your website is bumped to the second or third page of Google search results for your game if you're lucky!
I just did a random Google search for one of the Big Fish top 10 games (that wasn't developed internally) and not only does the developer's site not appear in the first 5 pages of Google results but also the piratebay, rapidshare entries rank higher. Essentally meaning that even if the developer had a direct sales business (they don't) they wouldn't be getting sales anyways.
Let's not forget the piracy issue - so not only are you letting your game be sold as a disposable commodity (and sacrificing direct sales) but you're also giving your game to thousands of hackers who are already sitting on key generators because the portal's DRM strategy is hopelessly broken.
It used to be that if you got listed at all then you had some decent money. Then it was "as long as you make the top 10". Now you have to hit the top 5 or you're better off with a day job.
How far can the odds diminish in this lottery and still have people play?