Grad school GPA inflation is only dependent on the type of grad program you are doing.
first let me say Kriss is partially right in that everyone has a ugrad GPA but not all have a grad GPA so that gives a level field for comparison.
Now consider that ugrad GPA requires a lot more competition among students whereas this is not true among grad programs outside of SMP and even there most SMPs are only 20 students outside of the 3 oldest programs so there is not competition. The courses are not graded on a curve against each other in any SMP only against a medical school curve whereas for ugrad you are graded against your peers.
Thirdly, people rarely if ever fail out of their grad programs and if they do they wouldn't have a degree with anything less then 3.0 whereas a 2.0 still grants you a degree for ugrad. So some people feel that they can't gauge an equal comparison.