well, that's not necesarilly true.
Of course the guess of chipn is completely correct
but you have to consider the possibility that the
bidder just didn't take a look to the new maximum
bid and didn't realize about it and gave up just
when yahoo shows the screen telling you that you
are outbidded and asking if you want to place
another bid.

It has happened to me a couple of times. Once i
lost the auction because of this and the second
time i got a bit lucky because i placed my bid
like an hour before the ending time. When i saw
that i was outbidded i just gave up and went away,
but just before the auction ended i wanted to know
how much was the item going to arrive, and at that
moment i realized that my bid was tied with the
one placed by the previous bidder and so i just
had to place an small increment... and i won the
auction....