Let’s Be Perfectly Clear…
4K or Ultra HD televisions are up-converting the incoming signal to 4K resolution. They are taking 1080P, 720P, 1080i or whatever signal you are sending to them and letting you watch a 4K image. Just like your old 1080P set took whatever resolution you sent it and up-converted it to 1080P. OK, so right now there is very little 4K content available but you still get to watch 4K.
Netflix, Amazon and others will begin streaming 4K content this year. Sony has a server that you can purchase and download movies (pay per movie) in actual 4K right now. But even if you are just using an antenna for over the air broadcasts, you will be viewing it in 4K on your new 4K/Ultra HD television or projector.
If you see a 4K set next to a 1080P set and there is not a big difference, then the 4K unit is not set up correctly. There is a difference and it is significant.