Here again, I think you assume that your own ability to pay for a sleeper is what the general public can or cannot pay. Just because $400 is your maximum price that you would pay certainly does not mean that there are others out there that will not pay higher. Sure, sleeper prices have increased, but I have yet to observe any noticeable slow down in sleeper bookings. Trains still sell out, often times with their sleeper sections first. Is the $488 price for a roomette from NYP to CHI too much for you to pay? Maybe. But obviously it's not for others, since there's only one roomette left on the particular train I priced. Same goes for $898 to book a bedroom on the LSL. Expensive? Sure. Is there only one left on that particular day in June? You betcha.
I still think this comes down to whining. Poor little dlagrua can't get his cheap sleepers. It's supply and demand. There's only one train per day in most cases, sometimes fewer, with limited accommodations. Ridership is up by almost double digit amounts. How can you get mad at Amtrak charging more for its sleepers if they're still selling them? Amtrak is a business after all, and if sleepers are hot commodities that sell out regularly, what kind of business would not want to raise prices to reap the financial benefits?
Bottom line: if you want a sleeper, you better be prepared to fork out. Otherwise, Amtrak will gladly sell that room to another passenger who is willing and able to pay the price.