From my few experiences at open source software programmery events over the past few years, I'd disagree. Always seems that a little fewer than half of attendees have macs in front of them. I explain part of it to myself by noticing that the numbers skew even higher than half when it's something 'webby,' and attributing that to the closeness to graphic design-media-marketing types.
With other systems programmer types, I still see plenty of macs, but I blame that on the fact that those programmers are spending all of their important time on the server and some don't feel like futzing around on their laptop with a more fiddly OS like Linux or Windows. The only thing that all programmers seem to like to fiddle with endlessly is IDEs and text editors, and there seem to plenty of mac options for that.
With other systems programmer types, I still see plenty of macs, but I blame that on the fact that those programmers are spending all of their important time on the server and some don't feel like futzing around on their laptop with a more fiddly OS like Linux or Windows. The only thing that all programmers seem to like to fiddle with endlessly is IDEs and text editors, and there seem to plenty of mac options for that.