Ask HN: Why do developers often use a Mac?

I've been seeing more and more posts where people are using Mac's. For the past few years I've been a windows user, with Linux experience mostly from server management, and seeing so many people developing their applications using a Mac has started to finally mess with my mind. I really want to know, why do so many developers, including web developers use a Mac? I can understand that having a usable, stable Unix environment can be great, but is it worth the large price tag to purchase the hardware, especially with Apple products getting less and less expandable?