nolimit, your computer monitor is plasma? Or LCD? There's a pretty big difference, both in quality and price. I've seen a few LCD TV's that are 40-50" and yeah, they look good. But about the same as an HDTV rear-projection TV. The thing is, most stores not only leave their TVs on non-stop, but they also don't reconfigure them when they're moved or bumped. So you get blurry screens and washed out colors because the floor models are pretty beat up. The TV I have looks just as good as a high quality (read- $7000) LCD screen at the same price, and although it's a bit bigger, it's something I can afford.
The thing about putting plasma screens on the wall is only due to their depth, being a few inches. They still weigh a good 70--100 pounds, which, granted, is about half of what a projection TV weighs. But it's not as trivial as just "hanging on the wall" -- you need mounting brackets and a quality wall to mount it against (not to mention be able to make pretty good-sized holes in the thing).
The reason that plasma doesn't look as good is because plasma works by essentially lighting up all of the plasma, which means that blacks don't look as black as they should. Normal TV's do it fine because black is simply lack of light -- nothing shines there. LCDs are also good, but the ones that aren't top 'o the line have problems with high contrast, as the white "bleeds" into the black, causing some ghosting.
And hem, we're talking about the rear projection TV's. regular TV's don't show up in retail in much of anything over 40".
I know someone who recently purchased a 94" front projection system. That's simply a high-quality screen you put on the wall, and a ceiling mounted projector. It's HDTV, extremely high quality, and cheap, too -- it only cost him about $2k (for 94"!!). The whole system is also much lighter than both plasma and LCD, as the screen is separate and very light, and the projector itself is simply stuck to the ceiling. But due to the separate components and the extremely large size, you really need a lot of space for it. You know that motion sickness warning in the front of game booklets? You start to feel that after long gaming sessions on a 50" TV -- imagine on a 94"!