Matt,
I always try for a variation of fw widths, even so far as to start the design with a goal of 25, 30, 35, 40, 45, 50, ad 55 yards wide on each nine. Hardly ever works out quite that way.
The idea that fairways should be the same width is a tough nut to crack. Did some grass lines last month and when I tried to go wider on one they wondered why. Also, one wide line brought back in after I left to "keep in line" with the other fairways that are about 35 yards wide. (BTW, the wide one was on an uphill 490 yard par 4 from the tips, so I felt justified)
And, in this day and age of cost consciousness, at least some of the objection is based on the cost to maintain "extra" fairway that isn't "really necessary."
Sometimes, its a matter of the clearing (or lack thereof, to keep a corridor to 2 row sprinklers) or even just the scale of the golf course. If a course has 4-5000 SF greens, sometimes ultra wide fairways just look out of scale.