Nothing, inherently, except perhaps the fallacy of comparing a pair of jeans to the rather chaotic and unpredictable world of bespoke systems development. One is inherently known (a pair of jeans you've presumably already manufactured), the other is one big unknown, basically.
He compared to jeans because they're an extremely trivial purchase that someone would give little thought to, but still demand to know what they cost. The point is that in all cases you need that information, with a major software project you simply need it far more.
And that's the core of the problem (which, ironically in the context of the article, agile methodologies were supposed to address): wanting or needing something to be true/exist doesn't make it so.
