I can't really comment on whether the test has been getting harder, as I have only taken it one time (a few weeks ago).
I did notice that, based on percentiles, a lot more people are doing well (very well actually) on the math section, while fewer are doing as well on the verbal.
For example, top score in math is supposedly 52 (though I think the highest I have seen reported is 51). A 48/51 is only the 86th percentile. That means that about 14% of test-takers score 48 or higher on math. The way I see it, it is EXTREMELY difficult to distinguish yourself in math on the GMAT, and each point you gain from 47-48-49-50-51 is a real challenge. On the other hand, I do believe tha most people all around the world can prepare for the math portion of the GMAT in 2-3 months time.
On the other hand, it appears that there are far fewer ultra-high scores in the verbal section. A 41V is the 93rd percentile (48Q, 41V was my score so I know the percentiles), so only 7% of test-takers score 41 or better. The difficulty, of course, is that I think for many people, especially non-native speakers, improvement on the verbal section is a slower process than improvement on the quantitative.
I guess the bottom line is that you must do well on the math portion of the GMAT, but it's very difficult to distinguish yourself there - many other people do well. If you can do well on the verbal section, however, I think you can distinguish yourself from many other test-takers. A 48Q and you are in the 86th percentile; but with a 48V you are well into the 99th percentile and it is rare indeed to see such a score.