Even though I mainly see our stats, I have a lot of data from some of the successful devs too, that underline my theories. A good example is selling your software only through PocketGear and directing everyone there would land you with less than a third of sales than doing the same with Handango - even if you're nowhere near the top lists.
"You also have exclusive 'showcase' deals": You mean the paid advertisements we run on Handango? They're not at all exclusive to us, they offer the same for everyone. You can also get SOME free advertising from them when you release a new product, and that's all documented in the devs section there. But for the bigger part, we pay for the advertising. It's not cheap, but it's almost worth it

I'm not saying everyone will sell thousands of copies through Handango. It's a small market and you have to make good products and do good marketing. Handango won't do all your marketing for you, but they can take a big part in it.
Cheers,
Peter of PDAmill