Macs have had the ability, even is somewhat unscientific, to have as many 'screen' profiles as one might desire. Simply use the Display Control Panel (OS9) or the Display pref panel in X. There is an "advanced" checkbox on the first screen but I always used that, so I don't know what you miss if it's
unchecked!

It's a very subjective process using the 'sit far from the screen or squint' methodology (well know to those who often sit on the back row!). But it does much more than the overly simple "brightness" slider. The next to the last screen allows one to set the gamma. 1.8 is (currently) labeled as "Mac" while 2.2 is shown as PC. What is/would be new is that gamma would become the Mac 'standard.' Apparently some apps change that or expect the number to be 1.8. Those that change it should but may not return the value to whatever it was before their usage. Those that expect one thing should remember Apple builds the boat, so don't expect to always have a 'portal!'
I think it is apparent that Apple expects 'professional' to use 'professional' color monitors and that requires a desktop
and an indoor room, preferably with controllable/adjustable lighting. I wouldn't think anyone would confuse an iMac as a 'professional' color manipulation machine. If one
must use a laptop, the pro models still are not made, exclusively, for those working in photography, much less color, IMHO. Checking for fine focus is one reason I've heard photogs complaining about the new portable's screens making things harder. How does one check for focus with a device limited to >150 dpi?!

Obviously, I no not of what I speak but that's hardly ever stopped me before!