TI's advantage is in their software. Anyone who has actually tried to get through a math course using a general-purpose computer knows what I'm talking about. Sure, Maple, Matlab, and Mathematica will all compute faster on my $300 netbook than my $200 TI-89, but it's so much easier to enter the equation into the TI, the total time spent is less.
If anyone has had a different experience, please share with me your resources for learning how to use the software.
(It's not like I'm bad with computers, either; one time I found it easier to write a C++ program than learn the equivalent Maple code.)