Some of the comments to my initial post suggested that compression in LSAT scores (for which I have only anecdotal evidence) is not necessarily a bad thing. For example, some folks noted that there is a signalling value that makes it easier to apply to schools where you are likely to get in. This is true, although I also tend to agree with the comment that the application cost is such a small part of the cost of law school that this is not a major factor.)
There are some reasons to be concerned about compression.1) The LSAT measures the ability to take timed multiple choice tests very well. (My coauthor, Bill Henderson, has an excellent paper on this subject.) Having a law school that is homogeneous in this dimension may not be a great thing. Or it may not matter.
2) A school with a compressed LSAT range is going to find it increasingly hard to move its median LSAT up (conversely, it won't slip much). Since schools put a lot of weight on the median LSAT, a lot of resources are going to end up being spent on trying to get even a very small shift. (I suspect that a rational strategy for many schools would be to focus on the GPA numbers rather than the LSAT numbers; although GPA is weighted less than LSAT by US News, there may be a much greater ability to move the numbers.
3) The shift to the 25/75 percentile numbers (or, more precisely, the average of the 2) means schools are now going to be paying a lot more attention to the keeping their 25th percentile up. That is likely to make it less likely that someone with LSATs below this year's 25th percentile is going to get in next year.
4) Compression has consequences for how law schools allocate scholarship money - one strategy is to spread money around among the people just above your median, in hopes of pulling it up. This means the people paying full freight, i.e. those below the median, are subsidizing the people above the median (assuming the school gets most of its revenue from tuition).