It depends on which developer groups they used. It seems certain web languages attract people who use Macs, where this data probably came from.
What is weird to me, is under Software we see Windows 7 and even Windows XP but we don't see any form of linux.
It could be that the interviewees used several different distros. So Linux would have made the list but splitting it into distros makes the numbers for each too insignificant to be in the top 10.