When everyone does badly and the professor says he or she won't curve they are lying and just scarying you so people will study more.
The reason they have to "curve" is because they have quotas to meet, especially in large classes. for ex/ 20 -25 pecrent A, A-, 30 pecrent B's? etc. If a professor gives everyone C's D's and F's, it will defintely count against them, as will giving everyone A's. They want the grade distribution to be spread out.
I put "curve" in quotes because there are different ways to curve the grade. For example, if a 90 is an A, and a professor doesn't have enough students (maybe 5 pecrent when it should be roughly 15-25 percent) in the A range after the first exam, the professor could just make the next exam much easier, and therefore, technically he won't have to curve anyone's grade. It's all based on how other people in the class are doing. If for example, a 90 is an A, and after the first test you get a 90 while the class average is a 95, you better worry cause you are in the bottom half of the class, and next test is gonna be a whole lot harder.
In FrozenTexan's case, I assume that it was a very small class, maybe 5 people?, so those are usually graded differently (no quotas), because obviously in a hard course like that and only 5 people not every teacher is expected to have genius A students. Also he obviously did end up curving if a 53 was a B-, and theres not much he can do for people getting 33% or below.