I think that evaluation of an undergrad transcript is far more than what your total GPA is for the admissions people. It can't be as black and white as the average GPA they list in class profiles indicate. Also it is one of the few parts of your application that you have no control over improving so dont stress over that part of it. I would think that the reviewers take a look at how your grades went, did they get steadily better or did they get worse? Did you have a horrible semester that you wrote an essay to explain why? Was your first semester a result of culture shock and being away and your only weak one?
Also one would think that over the years and with past experiences a lot of grad schools have at least a sense of what big undergrad schools provide in the way of a GPA scale. I agree that a 3.8 at one school may be a lot less at another, if both are known by a grad school then they probably have an idea that one scores harder than the other. It works the same for professors, in my fluids dynamics there were two different professors...one was an extremely tough grader, I had to work hours a day to get a B+ and my roommate had the other and never did anything, all the kids could coast with B-s just for showing up and doing all their work no matter the quality. I know kids who literally did it in the room before the prof showed up.
I think it also plays into majors too. Though not many people would admit their major was a lot easier than another...there are majors that are very demanding. Comparing different types of engineering there is a large difference between Electrical and Civil at a lot of schools. Not a slight to Civil but electrical is considered a very demanding degree to obtain. Now compare an engineer with someone who majored in sociology and its even more of a difference in the overall difficulty.
I would also think that the overall size of a persons course load would be taken into acount. I know I took over a years worth of extra credits during my undergrad, I was well beyond what was required for my degree and my minor. To carry as many courses in a semester as that required I had to have permission from the dean and department head. Had I taken the base requirements and chosen easier electives my 3.4 could have easily been a 3.7 or 3.8.