To be fair in your analysis, you also need to consider the cost of servers, support, add-on services like email notifications when there are issues, time spent to handle the same newbie questions from 3,392 newbies as they come on board and refuse to read the FAQ's, leakage (fraud, theft and criminal diversion of funds), the cost of absorbing pool hoppers (depending on the pool payout model) the equipment that they themselves host on and moderate their pool from, and the electron juice that feeds it all. Many pools also make good from their own pockets if there is a fubar moment, like a certain pool that switched pay models at the same time as switching hosting services and crashed some records.
If you want to get rich with BTC, I would suggest that there are far easier ways than running a pool and making a 1% rake off the top. An average pool that is running at around 30Ghs, will statistically hit a block around every 66 hours. If they request an average of 1% in donations or fees (a reasonable average looking at the comparisons) means that a typical 24 hour day nets them .75 BTC per day. At today highest exchange rate of $9 US$ that's 28.4 cents per hour. I'm guessing that their server costs eat all of that and more up. I don't know about you, but there are very few things in this world that I would consider doing for 28.4 cents per hour (or just about 2,500 US$ per year if you want to do the math!).