There are schools that offer online courses with residential components. Open University in the UK is a good example. I've always thought the argument that pure math is too hard to teach online as rather fallacious. Schools do it. It used to be that all mathematicians were autodidacts.
I believe there is not enough demand for pure mathematics or theoretical science to justify an online degree. There is certainly a learning barrier, but anyone attracted to those fields would likely be more apt to deal with the added rigour. Why is it that MIT OCW, Berkeley, and other has lots of advanced course work in everything but pure math and theoretical physics. You can't find a blowhard physicist to tape their rambling on QM? You'd think they'd be lining up to be the next Feynman.
FWIW, UIS has a decent undergraduate math degree program online:http://www.uis.edu/math/
They offer courses in abstract algebra and topology (on the undergraduate level).
University of Houston Math Department website states they offer grad courses online.http://www.math.uh.edu/Matweb/grad_mam.htm
Admittedly, they seem like glorified senior level courses, but you might find a course or two.
Additionally, the following schools offer applied math and statistics courses online:http://www.amathonline.washington.edu/amo/http://www.cvn.columbia.edu/http://scpd.stanford.edu/publicViewHome.do?method=load
There are actually quite a few online applied math (and Statistics) programs. Graduate level applied math isn't exactly a cake walk. I really think there is little industrial demand for theoretical work. Numerous engineering programs (at prestigious schools) exist online as well. I imagine there aren't many companies that would pay for an online MS degree in string theory or algebraic topology. Remember there has to be enough demand to justify designing and staffing a whole online degree program.