How could this article fail to mention linux?
I am running linux on a dedicated htpc and it plays smoother and more consistently than any windows solution I have tried. While I do not use linux for my main computer due to incompatibility issues with some of my software, linux for htpc solutions is mature and up to date, and far more stable. Further, linux is far more customizable and less of a resource hog. For those less technically inclined, some front end software (mythtv and xbmc) offer cds with complete linux functionality that even people with no knowledge of linux can easily use.
As for macs...I do not know why anyone would use that for an htpc. Poor video quality, lack of software, and less support from forum users make is a horrible choice. That said, it is good for 2 channel music since it is easily capable of bit perfect playback out of the box last I heard.