Ben's asking for money to support the cost of processor power and bandwidth. He said as much in his post. As Jing pointed out, however, those things can often be had quite cheaply, and people are being asked to pay 15-22 USD apiece for them. Four or five such donations could support the site for a year, if Jing's assumptions are correct (they seem reasonable to me, though Alexa rankings aren't always very accurate), and this isn't even factoring in the donations (probably small, but worth noting) that Ben has received.

Of course, as you point out, Ben's time and programming effort are valuable too, and it's certainly reasonable for him to want to capitalize on that. However, that's not what's being asked for; there's been no mention of that. There's a difference between asking for help keeping the server running, and asking for people to pay your personal salary. When someone says "I need ten times as much money as this service actually costs," it's very reasonable to say "er, why's that again?"

Also, please don't get me wrong, I DO think Ben's time and effort is valuable, and worth paying for. Don't twist my words to make me seem anti-support. All I'm saying is that when one is being asked to hand over a fairly decent chunk of cash (for something that is typically free on the internet), it's not unconscionable to ask what one is paying for. Price breakdowns are requested all the time in the retail world, and I don't see anything wrong with requesting an itemized receipt.