The ranking formula is points divided by submission age raised to some constant. This means that a relatively few votes in a short amount of time is all it takes to outrank much older submissions, even with many more total votes. 9 votes in under 20 minutes will do it when the majority of other front page submissions are many hours old.
I'd say it's more "The ranking formula is points divided by submission age raised to some constant minus a large value if one or more mods feel like it". Not implying some grand conspiracy here, but some posts disappear entirely if the mods think it doesn't belong, regardless of the number of upvotes or comments.
There is also the flame war penalty. If the ratio of comments and upvotes is indicating flaming, then the post gets some negative points for the purpose of ranking.
