I hate it when "technicians" say you need a box for HD picture. It's not a blanket solution and its pure BS. You may or may not depending how far from the transmitters you are and whether or not they have the channels you want.(There can be other things to consider but these are usually the big ones) Some, like HBO, Showtime, aren't available OTA. You would need a box from a provider, if you had to have them.
Some of what you bring up I question too. I'm not so sure cable broadcast is not HD to begin with but I can't dispute the few channels that definitely are broadcasting in HD and the crystal clear pic I get on those channels.
I'm about to get Direct TV or Comcast Xfinity, something that broadcasts everything HD and if I still need a box then so be it, I'll get one. I'll have to ask the cable guy when he comes.
You may need to pay a service provider, it all depends on what you want to watch and how far you are from the network transmitters. If you already have a UHF antenna, guess what? You have access to free HD programming already. If all the programming you want to watch is already supplied by an antenna, you just pay for electricity. The scam they've tried to pull up here where I live, is to tell people you can't get digital signals or HD over the air, you need cable or satellite. That's the BS i speak of. With OTA, you get razor sharp visual and uncompressed audio, not the soft pictures you get with some providers that try to squeeze more feeds into their allotted bandwidth and call it "HD" (Yeah, I'm looking right at you, Comcast) Most new TV's have the proper tuner already built in, so you don't have to buy one either.
It really depends on you. Some people don't care, if there is a picture and sound comes out of the box, its good enough. If you're like me and that doesn't cut it, like any hobby, A/V can get expensive in a hurry.
(This is just a really long winded way of me telling you that you may not have to pay for TV just because someone said you do. haha)