Why would anyone purchase Windows Server directly from Microsoft?

I wouldn't buy from eBay, you don't have the same counterfeit or audit protection as buying directly from an authorized reseller like CDW, Dell, HP, Software One, etc.

I agree that most organizations should never buy direct from Microsoft, but you should buy direct from an authorized reseller. Getting your server licenses from eBay is like getting your underwear from eBay. You don't know where it's been or who's already used it. It might be fine for some people, but it's not for me! By purchasing from eBay, you run the risk of getting a TechNet/MSDN key, which is not meant for production, and you'll fail a license audit if you're even in that unfortunate situation. Plus, just look at the first few links. The sellers can't even use proper punctuation or capitalization. Are you willing to risk the integrity of your server infrastructure on someone that doesn't capitalize "I"?

Also, just so you know, the list retail cost of 2012 Datacenter is $4,809 USD per 2-socket license, not $2,500. If you can find them from a legitimate reseller for $2,500 USD, buy it now!