Because when you pay attention to what's going on in a community, you notice trends. In the open source community, most notably the web development community, there has been a trend of moving to Mac.
I think you might have missed the point of the post you replied to. The point is that sometimes you don't need data. For instance, in the fashion world, one might notice a trend of people wearing a certain style of jeans. Nobody is going to go out and do a a random sampled study to see if this holds up to scrutiny, but the trend is noticeable to anyone paying attention. If you're involved at all in the open source web development world for example, it would be pretty hard to miss the trend of developers moving to Mac.
