They may throttle ports used by popular p2p filesharing software, but that is easily overcome. I doubt they will throttle bandwidth on any specific user. In anycase, it is difficult to say with any certainty what is the issue if one is using P2P performance as a gauge.
I've always been able to get full download speeds on all http/ftp downloads for the past 8 years and that I believe is a more accurate measure of whether the bandwidth is present.
I am just guessing, and it is not difficult to see the logic. If I am the server admin, if a user has very high speed link and continously download from my server, it definitely will deprive other users from accessing and may slow down other users. I would start to investigate what this user is trying to do. Bandwidth is expensive. I need to buy bandwidth from the service provider to host my webserver. If a user is hogging it, then others maybe affected.
May I know what is your speed? I am surprise if you can get full download speed if you are having 3Mbps. If you have 512kbps, then it is easily fill up. Also it depends on timing, during peak period, it will be very difficult to get full download speed as it will likely to be congested. Also it depends whether its local or overseas. There are too many factors..
Anyway, but if you are satisfied with what you are getting, then its all right.