On Mac OS 10.9.1, I have two different numbers for identically-sized frames, with windows in each equalized using M-x balance-windows. 70 in Emacs 24.3 and 71 in Emacs 24.4. It looks like a problem with the window-width function. Take a look at the attached screenshot: it shows the different return values, but it also shows that both windows wrap the new line at the 70th character.

So I guess term.el has nothing to do with this, it just happens to react particularly badly to the incorrect value returned from window-width. I wonder if this happened because of the change in using the Core text font renderer on OS X.