No, not quite.
Terabytes? not even close. Many may have as many as a couple OC3s (155Mb), or OC12s (622Mb), and the huge ones, maybe one or two OC48s or OC192s (2.4 and ~10Gb). Divided up by how many users? Hundreds of thousands? Millions?
Then, beyond bandwidth, there's the capacity of the active infrastructure and finite processing ability of the system. The closer to capacity they run, the latencies start to grow, and the system slows down.
The cost of redundancy, staffing, backup (power, environment, media, bandwidth ...) has to be tossed in as well. Riding herd on a bunch of wannabe webmasters / junior hosts just adds to the cost.
With rare exception, most of the providers, DSL, BB Cable, or dial-up provide the user with some webspace - put your server there; it's probably more secure and less likely to be a nusence (when your personal site gets hacked or infected). Need more space? Pick up a hosting package - there's some out there that are literally dollars a month. Picture hosting, Anon FTP, web, mail .... usually all included.
For the most part, this is a reactive industry; the caps are there because people abused the privilages and bandwidth. They are there so that "regular" users can enjoy what they've paid for (at the level they've paid for). If you want more, buy more.
If the providers can't make money on the deal, then you'll have nuthin' but dial up ... wouldn't that be a hoot. File sharing gets real easy: "For a good download call (345) 555-1234."
Pardon my rant, but this is one of my pet peeves. If you knew what it cost in equipment, personnel, and money to bring up, run, and maintain a system of any size at all you'd appreciate what a true pain-in-the-a$$ junk do-nothing servers can be.
JM.02
Scott