its true that 17" do have good dot pitch but for example if you look at the 2 dells above they have better dot pitch than your average 17" and they're 20".
17" tend to have worse contrast ratio because they use exclusively TN based panels where as an accelerated MVA or SIPS panel will be double or triple.
However I do agree that ergonimocally 17" is better for you, health and safty guides always say use a small screen to reduce strain.