They aren't really giving them away free. It's free with a contract and you still have to pay the $35 activation fee. At Amazon, you can already get the Eris and the Ally for free, and the Droid only costs you $20, and I'm pretty sure all of those come with Activation. So that deal really is not that good. And by the way, CNet is not giving away the phones, they were just informing people that Wirefly had the deal going on.
And to address your last question about about how manufacturers make money, it's not the manufacturers giving them away. The manufacturers make them for Verizon or any other carrier, who then sells them whole-sale to other retailers, such as Wirefly. Wirefly is able to give them away for free because they still profit due to the money they get from Verizon for signing people up for the two year contract.