Honestly, if the resolution is all you care about then you should just buy a high end PC with a good monitor and a high en graphics card that supports higher resolutions.
It's perfectly fine to own a PS3 without an HDTV, though of course most of their selling point when advertised is the HD output and format but you really don't need it to enjoy the games. The same goes for the 360 in my opinion.
Keep in mind that doesn't mean you won't want to get one, I had wanted an hdtv since I'd gone to my friends house, I like big screen and wide screen for that movie feeling so it was simply a natural step for me. Don't feel like you have to get it right away or ever, get what you need to enjoy yourself and nothing more. If you feel you need a HDTV just chill out and wait around for a good sale.
