I have a 42" 480P plasma (850x480) that blows away almost every single HD LCD I have seen.
I also have a 720p/1080i (1360x768) Viewsonic LCD that doesn't even compare to the picture that comes out of my 480p Plasma.
picture quality is definitely not 100% directly related to how many squares are on the screen

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However, you are looking to compare apples with oranges. Plasma and LCD are two completely different beasts. It really comes down to personal preference. People see things differently. Some think just because the screen is "brighter" it has a better picture (psycological). Others will think one tv looks better than the other just because they know going into making the decision that one has a higher resolution than the other.....
They should do the pepsi / coke challenge. On one side a high quality 480p and on the other side a 720p. Don't tell people which is which and make them stand 6 feet away and make a decicsion on which tv has a better picture. It would be interesting.