i think ur slightly missing the point of the credit system. The reason it works better than u think it does is because emule shares files while u r downloading them. So when u get a chunk of the file and someone else downloads it from u, then u get preference for getting more of the file from them and this happens with all the people downloading or uploading this file, also the link to the person u uploaded to is stored (even if u or the other person goes offline) and emule automatically requests any parts of the file u don;t have from them. Since emule can sit in hundreds of queues at once, ur chances of connecting to them again are probably around 1/3.
However, one point that was being discussed when i was last at the emule board was 'getting into the loop' cos until u get part of the file u just sit there waiting at a disadvantage in queues. Also once u r downloading a file it is probably advantageous to disallow access to ur other files cos then all ur uploads are of the file u r downloading and so u build up credit with people more likely to have parts of the file u want.
But i'm sure they've come up with solutions to these by now cos i haven't been using emule for ages