I spent some time reviewing the pictures on the Sony and the Samsung in all modes of reception. In SD, the Sony is measurably clearer. I have had the dealer place the TV's next to one another for the test. In other modes, the difference was much closer. In general, the Samsung was brighter, but the Sony was slightly sharper; but in a room by itself, either would by agreeable...but not in SD.
I would look into the Samsung LED DLPs. They can be had for a reasonable price and the half-life on the brightness output is 25,000-30,000 hours. It's also EnergyStar rated and quiet.
Any difference in picture brightness can easily be manipulated. If you're comparing them in store, you're doing yourself a huge disservice. They never set them up properly and most likely just opened the box up and set them on the display floor without any adjustment. Brighter does not equal better.
Snacking -
You say that your father is slow to pick up on the HD programming. Why? All the major broadcast channels have an HD station and the Samsung has an HD tuner built in. Easy enough to pull them in and then watch it. Heck, I get three, THREE PBS channels in Phoenix being broadcast on the digital spectrum (off an antenna made of coat hangers and speaker wire). Cable only brings me one.
HDTVs make SD programming look horrible. End of story. The picture is clearer and any defect in the picture/signal is magnified. Don't let your Dad off easy on this and force the issue. He'll thank you later. 4:3 programming is basically obsolete, so, he had better get used to the 16:9 format soon.
I'll bet that he's intimidated by the new technology and doesn't want to change. Life happens and that's change.
-pat