For YEARS Pro tools sucked on PC and was just not a viable option. Also PC's sucked in general for audio so most studios went the mac route and never looked back. I have no issues with PC's per se but I would say that macs are still built a bit better for audio/video.
Second Pro tools is a more appropriate tool for a recording studio that works on many different projects in a day, Records live music, mixing film scores, ETC (I would never record a band with FL for example) If you want to work in the music industry especially in a studio you sure as hell better know both macs and Pro tools (and Logic to a much lesser degree.)
As far as video goes there is a major shift to Final Cut and that of course is mac only. Apple builds so many technologies in to there computers that are for content creators.
Now as far as FL/Reason goes they are more songwriting tools, Reason is widely used in top 40 music and I have never seen anyone look down on it. FL has a little bit of a unjustified reputation as being a toy but is a fantastic tool non the less.