It's apparently different at my undergrad program - different classes are graded on different scales AND different curves.
I'm currently in a two-year honors biology program, and we are held to a strict:
A: 90-100
B: 80-90
C: 70-80
D: 60-70
F: 0-59
And ABs and BCs are given at instructor discretion.
In most of my other honors level courses, the course is curved on each exam (if the highest score is a 50, that's an A) because the tests are written to be extremely challenging and really push the edge of your knowledge, or the course is curved on a historical curve because the material is so equivalent, but you will always get fluctuations because of the fact that the tests have different questions every year (i have a class current that ends up giving an A for roughly 86%-90% and above depending on that year's curve). There is also usually an altered scale of some sort that pegs percentages not at the standard 90/80/70/60 points for A/B/C/D based on how/whether tests or final grades are curved. The average tends to be a B, with a fair number of As and Cs given. Student performance is usually quite high, so I don't believe there is inflation going on, and I have had a professor decide to simply give out more low grades than usual because student performance was quite low compared to normal.
Most non-honors courses stick to the same scale as the two-year program, and there is usually no curving.
GPA is:
A=4.0
AB=3.5
B=3.0
BC=2.5
C=2.0
D=1.0
F=0
Most degree programs require a 2.5 to graduate, and the honors program requires a 3.3 (which I don't understand because we already have to take exceedingly more difficult classes... /whining because I have a 3.2 because of a fucked up situation lol).