Users really do need their own personal T1-lines for browsing the WWW. At least, they need access to the full bandwidth of a T1 line whenever they request a new page. This can be seen from a simple human factors calculation given the common finding that hypertext browsing requires response times of less than one second for the user's navigation to feel unencumbered.
A one-second response time requires that the user's system can download the page in less than half a second if we assume that network latency across the Internet is about 0.5 s (quite an optimistic assumption for many connections). Many web pages that contain a reasonably-sized image are about 100 kB in size, and thus require about half a second of a T1-line's 1.5 Mbps.
Voila! Full T1-speed is required for acceptable web response time.
Of course, in real life, several users can share a T1-line and still experience one-second response times as long as they don't all sit frantically and click on hypertext anchors as fast as they can without reading anything on the pages.