#1 Mark
As far as I can tell, the only difference is what you have noticed: one has the dual tuner and the other is a single tuner.
When you connect a single RF cable from a roof antenna to the single terminal on the model with the dual tuner, LT27HV, you can tune in two broadcast signals so that you have two local TV programs running in PIP or split screen.
I have the 30" Olevia with the dual tuner. I've noticed that, when you do the Setup after selecting "TV", you will get to auto tune for local over-the-air on one tuner and to auto tune for a cable TV input. I don't have cable TV, so I don't know how this really sets up. But, I can get all the local TV channels from each tuner.
Dual tuners add some viewing flexibility. You can watch two live TV programs at the same time, if you want. For example, I watch simultaneous, spit screen live baseball from the Baltimore Orioles on local channel 66 and from the Washington Nationals on channel 20. You don't get simultaneous audio; the audio switches as you switch between TV programs.
I suppose the single tuner version only permits tuning to local TV stations, and not cable. I'm just guessing on this.
But, that's about as much as I know.