Just because there are loads of seeders / peers doesn't mean they are in fact all available. A peer does not have the complete file - they could well be trying to download. Many seeders (and peers) will restrict the number of connections they allow so their client doesn't get overloaded - after all they too only have so much bandwidth. Trackers may list all they can see, but the clients will reject anyone too far away (high pings etc).
Remember to give if you are to receive. A good sign that everything is OK is when you see your upload is working too - you should on 4 meg be capable of around 25KB/s upload without oversaturation.
& of course, you are only downloading these files as backups aren't you - we can't be seen to condone piracy
