This is nonsense.
TV is watched on a television, which is usually a product designed to overcome ambient light. A theater is designed for the utmost in light and sound control so that you see and hear exactly what was intended.
If a guest needs to take a break that is what the pause button is for on the remote, which then means you can turn the lights on. If you wanted something in the 75" size range that can handle ambient light they do make televisions for that application.
Otherwise you could have just bought a five year old project and not noticed you were not going to get the black levels that light controlled rooms afford.
Dedicated home theater. No, we watch TV in the living room. If we do watch TV on the big screen, we do so in the dark or knowing that there is a compromise in watching with light. Not sure why guest would be stumbling around in the dark? You can use floor lighting or just pause movie if someone needs to get up. My lights are run by my remote. No stumbling around.
What I do is a bit different. I run a plasma behind the screen. Its a motorized screen that drops down in front of speakers and plasma.
Yes, I'm reviving a thread - it's not THAT old.

[oddly enough I stumbled upon this while googling, and as you can see, I didn't make an account just for this post! lol]
With that out of the way, I just have to find this attitude remarkably annoying. Why? Sometimes the magic of a freaking huge projection screen is being able to host sports parties with a massive freaking screen. Who wouldn't want to watch, say, the Super Bowl, on a 100" screen? I'm personally considering a projector in the not so distant future (couple years most likely, could be within 12 months, who knows...), and the option would be my 50" Plasma likely behind a drop-down projection screen, or said projection screen. A room full of 10 or so people, of various distance from TV, I'd personally vote to have the projector up and running in such a scenario. But that kind of scenario is also decidedly NOT one fit for a dark room. And sure you could pause but the idea is to keep watching live.
It's not so much complaining about the limitations you fully understand, it's more just griping and moaning that there isn't something perfect out there yet. That's my take at least.
Eug, how's that projector working out for you anyway? That's a model series I've been eyeing, along with JVC's D-ILA line.
[Mods, please don't hit me. At least, not too hard!]