I guess it depends on the quality of the sapphire crystal. I doubt the sapphire crystal on my $300 Hamilton Khaki is as hardy as that on a higher end watch.
I'm pretty sure the Tag Heuer Monaco doesn't have a sapphire crystal. It's acrylic or perspex, as a testament to the original Heuer Monaco. Hence it'd scratch really easily and chip. But the scratches can polish out and chips can be filled in.
As for the Rolexes, well yes, a lot of them have the same base movement. The equivalent Oyster Datejust in Stainless would be cheaper than a stainless GMT 2. GMT 2 costs more because it's got the extra complication (GMT) and is a sports watch in construction.
But for a $30K Datejust, yes it's the same movement as its stainless $5K counterpart, but by then, you're paying for the lashings of diamonds, platinum and other precious metals That's true for all watches I guess- same base movement, different complications and decorations push the price up.
Modified by Jules at 5:49 PM 12-10-2005