This quote "One needs about a doubling of linear resolution or film size to make an obvious improvement. This is the same as a quadrupling of megapixels." is not only subjective, it's flat out wrong. Theres a remarkable difference between a DVD (480p) and HD at 720p, and that's only a 50% increase in linear resolution in one direction (and only something like 15% in the other).
Well, like many things, the improvement is logarithmic. At small values, small increases make a huge improvement. I won't claim that his point is correct, but it doesn't seem unreasonable.
720p is still less than 1 megapixel, and has more than twice as many pixels as 480p. At such a small megapixel rating, the increase is certainly going to be much more profound than a 4mp to 8mp camera. But, perhaps doubling is a better metric than quadrupling.
