It's been pointed out, but 300-400 is still a pretty big chunk of change for a lot of people. But you're right, if you compare a full-scale dinner, sitter (grandparents?), multiple snacks, you're looking at $50-$100. Even at home people have to eat dinner, and you can get McDs whether you're watching a movie at home or going to the theater - likewise a steakhouse. Snacks and drinks during the movie you're definitely at a disadvantage going to the theater but you know, the theaters have to survive and the studios would be happy to take all the money and leave the theaters themselves to rot. But the tickets themselves, which we're comparing to the flatscreen, are still $25 or so. And that's assuming not-matinee or special pricing.
And "a decent-sized flatscreen" is one thing but I thought we were talking about a full home theater system like
@Ovation has and
@Mage seemed to be implying? That needs a proper projector and screen, full calibrated sound system, seats, plus the physical space to actually watch it in your home so no two-bedroom apartments most likely.