When using a comma as thousands separator in tex, one should wrap it in braces to avoid a spurious space after it (http://www.tex.ac.uk/FAQ-dec_comma.html). See below the difference between"$1{,}234{,}567" and"1,234,567$" withtext.usetext=True.

Unfortunately, mathtext doesn't implement this detail (text.usetex=False).

(It doesn't look that bad on these zoomed images but I think the difference is more visible if you draw them e.g. usingxlabel.)

(Yes, this qualifies as a major nitpick.)