Well, no, that's NOT weird. Normal web surfing and downloading are coming from dedicated servers. Bittorrent is not.
Bittorrent is coming from peers -- people just like you with computers like yours and connections like yours, and your speed is always dependent on how many of them there are, where they are, and whether you can connect reliably to them -- which is different for every one. This is the single biggest factor affecting your speed. It's also the one that is constantly variable, and the one that you can't do anything about.