As to the whole 720p LCD vs NES debate, i can say i was using composite out rather than RF, so maybe that contributes something? I didn't end up testing out RF, i couldn't find any adapters, and i had plenty of composite/coaxial (not RF) cabling handy.
I'm not experienced with reading schematics beyond an LED/resistor circuit, but judging by
THIS schematic, there looks to be some post-processing between the Video Line Level Out (RCA) and the Video RF out, before the RF Out RCA/TV Passthrough adapter.
Maybe it's nothing, and the house brand TV i bought really was crap. Just trying to help shed some light.