Dac, its dead easy..
The reason pro's use mac is because they're proven to be reliable, OSX and Logic on mac is a system im reassured with that it will not fail when recording. There is nothing worse then having a customer re-record a perfect session because the daw failed, stopped working etc and this is why its a no brainer for anyone in the bizz.
The performance isnt comparable either which has nothing to do with hardware but with coreaudio. For example, recording 24 channels through logic (ssl alphalink) + full on monitor mix with 1ms latency isnt possible (afaik) through windows.
Again, this isnt concerning anyone on this site since no one is recording bands for a living, but if you're out to get something reliable in the first place then its tough to get around those facts. There are some good systems to run on windows but they run on propietary systems like pyramix, samplitude or sadie which are really ffin expensive and are basicaly mastering daws that untill recently started to venture into the mix/recording domain (ergo, not there yet).
I work on either for years but if i have to do recording instead of production then its osx all the way. Production-wise im 80% on windows, either mac bootcamp or a $400 dell studio laptop not even using an interface (meaning im not using any hardware). When using hardware im using Logic because its still the best when using midi. Personaly i'd say that quality wise the hardware route still sounds best but production wise its just different than pure itb, not better because your approach to making a track is different.
Also, i think producing itb doesnt matter at all if its mac or win...reason or live runs just as well on either since latency isnt much of an issue here.
Also, the million dollar studios are a thing of the past, theres only a few that can remain succesfull to justify the value of gear they have, most gone bankrupt over the last few years.