Or you could just give in and accept that it's a tried and true method of delivering quality content and security!
I got over my distaste of pay to play with EVE Online - they're up to their eigth (I think) free expansion thats being implemented right now. We get all sorts of balance tweaks, new toys and updates - and even prettier graphics
Basically the infrastructure requirements for something like a good MMO require more than just a one-off purchace investment.
But it goes two ways - if they stop delivering an engrossing and top quality product - you stop paying and playing
I know I've been asking the gods of FPS worlds to keep on delivering patches and content long after the developers have moved onto the next thing... Look at WoW and EVE - been going strong for 5+ years.
Take the plunge