The official statement on undergrad TAs can be found here: http://brown.edu/Administration/Dean...Guidelines.pdf
If the admissions officers did say that, then I agree that it was misleading, as it is simply untrue (and TA-lead sections are clearly permitted by the faculty handbook).
I have recently looked into how other top computer science departments function without as many undergrad TAs as Brown's has (or with none at all). For the most part, their grading is automated, which requires a massive infrastructure and enough supervision to be sure grades are being assigned correctly. There is a movement in the department in that direction for a number of courses, but it's too early to say how effective it'll be, and the TA program continues to grow rather than shrink.