What purpose did it serve? The typo was in a commit message. Assuming that the committer ever even sees it -- most submissions here are not submitted by the original author -- he is certainly not going to go back and fix the typo in his commit message.

Besides, in 99% of "typo instances" it is quickly obvious that a typo was made, everyone understands what it should be, and continues on. If it's a typo that actually results in a real problem then by all means point it out; otherwise it just adds to the noise (such as in this case, where it was merely a transposition of two characters).