Alright that all sounds right. Your download speeds can range when downloading from websites because each website has different bandwidth, and set rates. These rates can vary especially if you are a free user vs a paid user trying to download this file. If you are downloading a torrent, your rates will depend on the uploaders connection.
If you have any other questions on this topic feel free to shoot me back a response as i'll be more than happy to answer any further questions you may have.
It has been forever since I have been on steam, but I believe that you can state your connection speed under preferences. Change it to cable, and maybe it will speed up. I would verify, but I am currently at work. It is something to try though. :-)