I know such always get critized by customers and it's Sony here... But lets try to look at it objectively. Running online services costs money. Running online services that are constantly improved, have new items or classes or whatever rolled out and the game being balanced all the time cost a lot more money. These games don't have monthly subscriptions because that only works with mmo games. This means the game company is fully dependant on the income from game sales. When people resell their game the game developers get nothing, so they also have less incentive to support online games.
Now this leaves a few options for the game company. Valve is currently experiencing with the another one - make the game free to play and have a store where gamers can buy items or decoration (hats, different colors). This is also how Facebook games and the like work, and this has been the standard in Asian markets for a long time. This also gets criticized here on slashdot, but I think it works pretty well with TF2. Players get a truly awesome game for free and theres incentive for the players to buy from store (I want this item now), but they can also unlock them via achievements and playing the game. I bought TF2 (Orange Box) when it came out, but I've also bought a few items from the store after I started playing it again now. Items I felt would make my gaming nicer as I could customize my classes as I wanted to. Items I just got a little bit earlier.
The other one sadly is either monthly fees or things like this PSN Pass. As I've personally never resold a game (and I don't think it's so huge market with PC games, consoles yes) I really don't feel like paying a monthly fee to play some shooter game. Microsoft handles this by collectively collecting a monthly feel for the whole 360 service. But the truth is, somehow the company needs to get money to run the online services. I spend a lot for the game, so I don't like to subsidize freeloaders. It's only fair that they also pay a little to get online access, which is a recurring cost for the game company.