I'd take the TV away, save for 30 minutes a day. I'd directly relate your sons unwillingness to engage with the world to his TV watching. TV dulls curiosity and creative play.
As to activities, I've had my 19 month old enrolled in three activities and a playgroup since she was 6 months old. We are out of the house 5 days a week, and we go to the park in the afternoon when nice outside. So no, we don't stay around the house, and this winter, even with a newborn (I'm due in 4 weeks), I plan on keeping her in her activities. I also plan on joining the DuPage Children's Museum so that we have someplace indoors to go. I also bought her a snowsuit and have little doubt we will be outside playing unless it's dangerously cold. My daughter needs to run around, and there is no way she is doing it in my house!