The round screen has nothing to do with NTSC or any particular styling. They just didn't have the technology to make a rectangular color picture tube correctly and cheaply enough.
I could care less about corner logos and text on the overscan. As far as I'm concerned TV was designed for moving pictures, not for reading news headlines or looking to see what channel you're on.
The point is the original color NTSC sets produce a way better picture than anything else today. More care was put into making the set during the 60s and early 60s than with their later rectangular counter parts. Just compare the reds on a 15gp22, 21cyp22, or even an 21axp22 with a later rectangular tube. The reds are much deeper and look alot more natural.
The only thing that comes close in reproduction to the roundies is the chromacolor seties, and its still not anything that close.
SO the factors that make me want to collect them:
1. extremely well made
2. brilliant color reproduction
3. --and they just look cool
my .02