Interesting; I'm a CS prof., where you can sometimes get away with that, but increasingly the expectation is really that you'll be funding several students out of your grant money, and at some schools, funding a portion of your salary. Baseline to get tenure at a research-oriented university seems to be about $500k-$1m of grants during the 6-year assistant position (i.e. enough to fund an average of 2 PhD students per year over that period out of non-TA/dept money).

It could be less in math because there isn't the same "lab" concept, where to be considered a "successful" professor you're supposed to oversee a lab of 3+ (better if it's 5+) PhD students, a post-doc or two, research scientists, etc.?