I have a Sony Bravia KDL HD850 that looks great with my apple computer but it seems to output different resolution when I compare it with my mbpro 2 ghz intel dual core from 2006 with leopard vs mbpro 2011 with lion. I have no idea why the two operating systems would cause such a big difference in resolution but it does, there is more detail and gradation in the mbpro from 2011, and more options in the display, it recognizes the sony tv and can adjust 1080p vs 1080i. the mbpro from 2006 only has default calibration settings. Both are going in via DVI to HDMI. Mbpro from 2006 is regular DVI to HDMI and Mbpro from 2011 is mini dvi to HDMI.
Have you considered the vastly different video/graphics cards that are in those two machines? 2006 to 2011 is 5 years -- an eternity in video/graphics card technology. Is it also not surprising two different operating systems three generations apart (10.5 to 10.7) are going to see changes and advancements?
So if I combine much newer hardware with newer, more refined (arguably) operating system and video drives and associated libraries, I wouldn't at all be surprised to see the newer system having more adjustments and better output. More simply stated, I'm not surprised that your newer computer is better/faster/whatever than your older computer.