...the LSAT is much harder to learn, but it's still a learnable test. So are IQ tests, of course.
...The SAT is easily learned, though.
What do you mean by 'learned'? Learned during the taking of it?
Learned through practice before the taking of it. In the case of the SAT and GRE, by learning vocabulary words and math formulae. In the case of the LSAT, by taking enough practice tests that one becomes accustomed to the sort of thinking required--not as easy, and there isn't as much room to improve (some people are just better at formal logic than others), but still possible.