"that's because you always say it and hear it that way.
for me, what and which is like much and many. which distinguishes one from a group, what is more qualitative. which is objects, what is ideas.
which car, not what car.
what kind of car, not which kind of car."
Actually, I don't believe the two are objects vs. ideas. I think what vs. which is a matter of restrictive vs. nonrestrictive. "Which" in that context is restrictive.
The links you gave do qualify for abuse of "which". However, in normal circumstances, the two are comparative. Here are examples:
What car do you drive?
Which car do you drive: Toyota, Hyundi or Honda?
The two are acceptable, except "what" does not restrict the answerer's choices. In contrast, "which" forces the answerer to choose between what is given.
Another example:
What is your favourite colour?
Which is your favourite colour: Red, yellow, green, or blue?
What is your name?
Which is your name: Scott, James, Kevin, Tom, or Luke?
Again, the first is nonrestrictive, whereas the second is not. "Which" assumes a restriction, whereas "what" does not. The answerer to the first could say "purple" and "Lisa".