Well, you could run it at 1440x900, and it wouldn't look any worse than the previous 15.4" MBPs...
In any case, as far as information density at the "1920x1200" setting, versus 1920x1200 native laptops... if we're comparing a 15.4" MBPR versus a 17" MBP, it's the exact same amount of information on screen.
If we're comparing a 15.4" MBPR running in "1920x1200" mode versus a 15.4" 1920x1200 Windows laptop (which existed in the Core 2 Duo era), the MBPR will have a little more information density at the same nominal point size, due to Mac OS assuming 72 ppi, versus Windows assuming 96 ppi. That does mean that a 12 point font on the Mac is 12 virtual pixels (at the framebuffer level, it's 24 pixels, and on the display I believe it's 18 actual pixels), or .082" tall, versus 16 pixels tall on Windows, or about .109" tall.
But, Windows tends to use smaller nominal point sizes, to make up for it, IIRC. And, web content is 96 ppi on OS X, IIRC, so it's a total wash there.