[notatoad]

a couple possibilities there:

1) if the first one performs well, people are probably ignoring the second for being a dupe.

2) a source website's reputation, page load times, amount and type of advertising, and site design all factor into the popularity of a submission.

3) luck is a factor. just because something does better this friday night, doesn't mean that every friday night is a good time to submit. the first couple upvotes are crucial, and that's only one or two people - easily within any error margin.

4) maybe i'm totally wrong. this isn't a scientific analysis, just my general perceptions, and i've only actively been reading HN for a couple months.