It's a commonplace to observe that average grades at some colleges and high schools have increased over the years, to the point that A is average and 4.5 on a scale of 1-4 is good. I think humans have problems telling the truth, so it's easier to shade the grades slightly, which over the years becomes more than slight.
But I just started to read a review of a history of girl's scouting in which the author talked of summer camps as being "middle class". Without being too nitpicky about it, seems to me that's "grade deflation". Surely if you had enough money to send your kids to camp in the first part of the 20th century, you were probably upper class, or at least upper middle class.
I think the logic of this deflation is the same as for inflation--making people feel good by calling them something they aren't. In America, "upper class" is bad, so we deflate the term.