The UK charts are ruled by 10 year olds at the moment, they are the only people who buy singles, it has got marginally better since downloads were incorporated, but airplay should be included aswell. I don't know too much about how the American charts work but they seem to just work better, artists stay in the chart for much longer, in the UK the chart is based on which songs the 10 year olds like that particular week, hence why a single doesn't (usually) stay in the chart for very long.