I submitted this exact article from the same source an hour and half before this submission. How does that work?
http://news.ycombinator.com/item?id=943346
Have a look at the actual URL. Yours has this on the end of the URL:
?utm_source=feedburner&utm_medium=feed&\
utm_campaign=Feed%3A+weblogsinc%2Fengadget+\
%28Engadget%29&utm_content=Google+Reader
EDIT: To clarify in response to ugh's clarification below:
It is not randomness that the duplication was permitted.
However, yes, it is (partially) apparently randomness that makes one submission appear on the front page and not another. My observation is that one submission may go unnoticed, and a duplicate does get noticed, up-mud once, and away it goes being noticed. If the first submission gets noticed, the second never happens.
The dynamics aren't difficult, really, although they are prey to the random timing of people looking and liking (or not).
I read his comment as “I posted this also, why does this submission appear on the front page, not mine?”, to which the correct answer is “Randomness.” (I think).