I'm sorry that this happened to you, but people do 
change their minds, though I would be very leary of 
a bidder with a zero feedback anyway.  
I suggest that in the future you raise your opening 
bid on your auctions to reflect what you want to 
get for the item and also for eBay's fees, this way 
you don't lose anything if something like that 
happens.
Too bad eBay isn't like Yahoo.  On Yahoo when a bid 
is retracted, the price on the item doesn't drop to 
the next bidder's high bid, it just stays at the 
highest bid.  Also the seller can retract the bid 
after the end of the auction.