The letter definitely did make it seem like it was more about a 'balanced' class than a ranked waitlist (though it did also mention LSAT and GPA) ... no sense as to how big the waitlist is, but anecdotally it doesn't seem like a good sign that I don't know anyone who got in.
On the other hand, given that they have a small class and probably share a lot of admittees with Harvard Columbia NYU et. al. (which are all ranked higher in US News, though it is questionable whether they are superior schools) it makes sense for them to use the waitlist pretty extensively (since it adds uncertainty to their expected yield).
Just wondering ... when did you apply? Have you applied / heard back from other 'Top 5' schools? What are your thoughts on submitting supplemental letters or recommendations? From the fact that they explicitly allow it in the letter I infer that it is probably helpful.