Although I agree anyone capable of scoring a 174 on the LSAT has a high natural aptitude for the test, I don't necessarily think that most people need 2-3 months to max out their scores. I reached a plateau fairly quickly as did a few others I know and from reading posts on here it does seem that although some people continue to make steady improvement for long periods of time, many others reach their max pretty quick. Its really impossible to say what percentage max out fast because we don't have a large enough sample and there are so many variables (studying methods, etc) but I know at least for myself that I don't think 2-3 more months of studying would have gotten more than possibly a point or two higher on the LSAT. That being said, I do agree I wish I had studied a little more because 1-2 points would probably have made the difference in some of the decisions I got that I wish were acceptances.
How long did you prep?
It's true that different people may take different amounts of time to reach their max. However, given that this is true, it would presumably make sense to give yourself as much lead time as possible, in case it takes you longer to do so. (In my experience, and most of the people I know, it did take awhile to really max out.)
Some people plateau for awhile, then make further increases down the road, especially if they take a break. But as you noted, even small increases can be helpful, especially at the upper ends of the scale.
Bottom line, if you start out 3 months beforehand, and get where you want to be in 1 month, you can always chill for awhile, and start up again a few weeks before the test. However, if you start one month before, and are nowhere close to where you want to be, you're pretty much screwed unless you can postpone for a later test date, or can wait a year.