LimeWire version numbers seem to work like this:

X.Y.Z

X == A huge major change.
Y == Updates to functionality that may introduce some bugs.
Z == Fixes for bugs that were introduced in the new Y version.

So, 2.7.2 doesn't add any new features from 2.7.1, it just fixes some resource problems and bugs that people reported. When all the bugs are fixed, LimeWire changes it from 'beta' status to official and updates their main download page, reporting the new download as X.Y, leaving off the Z.