It's doubtful that Giffen goods exist at all, but wine is a beautiful example of a Veblen good; demand actually strengthens rather than recedes as the price increases.
A bit off-topic, but there was a study recently claiming Giffen behaviour in China concerning rice staples. The classic textbook case of the Irish potato famine was always difficult (if not impossible) to prove, but this is apparently some evidence of the existence of Giffen goods.
I wouldn't go as far as saying the demand function has a negative slope during most of its domain, but it may have small segments with a negative slope.
But I totally agree with you, the evidence here shows that the wine market is ridiculous.
