When I first started in the design biz, I recall being chastised for putting a bunker about 30 yards short of the green, which I saw on old courses (I am told that before irrigation these served as frontal bunkers) and thought looked good. The late 70's prevailing wisdom was "they are out of play." I still do them now that I am on my own, becuase I think they look fine!
As Neal says, cost is an issue, although I favor high production mowing (ie no mounds) and argue that those cost savings equal out the cost of more bunkers. But where cost is an issue, I have a litmus test when deciding placement.
Bunkers can serve as hazards, targets, framing, safety features, or "save" bunkers. I try to put a bunker where it can serve may functions rather than just one. I also put them where they are easy to build (in a natural upslope) and clearly visible - the owner is paying for the sand, so why shouldn't we see it? I also consider whether the bunker blocks circulation to a highly frequented area of play.
Every course is different, every hole is different, but on lower budget ones, I have less tendency to put bunkers in the 180 yard range, or 30 yards from the green, for cost reasons.
I think Ross was replying to the typical golfer who loudly complains about a certain bunker, soley because they got in it!
Mark probably was trying to take the discussion to a higher plane, but those are some practical considerations.