Hi John,
Good point. I had the good fortune to spend some time in a working studio this past summer and the single most impressive thing was that it's dead quiet in there. Other than the sound generated in the room, it's almost as quiet as space, even the air conditioner was barely audible when it was the only sound and you concentrated on listening for it. I stepped into the vocal booth and pulled the door to, and the easily audible conversation that was going on in the main room disappeared completely. The control room had a very dead sound, so when you played back, you were hearing the monitors only, and very little of "the room". This is probably also the biggest single thing that separates a pro-level studio from the serious home-recording hobbyist. Most of the actual gear, including the real "go-to" gear is pretty much in reach for the average person, and there is a lot of inexpensive gear that does great, not to mention software, but the difference in environmental noise is still expensive to address, and treating the room requires specialized knowledge. And most people never think about addressing it anyway...
In this studio they used noise gates only sparingly, for instance, to cut off the decay of the snare drum to stay out of the way of the hi-hat. In the average home recording situation there's some trade-off between squashing noise and having natural sounding decays. The good news for computer recordists is, if you record in 24-bit and use proper gain-staging practices (which is another thread...), you should be able to get a signal-to-noise ratio that is acceptable for all but the most intimate recordings, and still leave plenty of headroom for processing, and to get that puppy LOUD, unless you live near an airport or something.