Joe,
I get the impression (if that is the full quote) that Mac says the Old Course had no definition, but then goes on to seemingly presume it is necessary now, and if so, then do it right, with flowing lines, and keep it short, etc.
If he was advocating for no definition in America (or elsewhere) wouldn't the second sentence just say don't have rough?
Do I have that wrong?
As to the widening out, Gary Player and other good players have written over the years that the FW ought to be wider at 300 than 200 out, on the theory that a 10 degree off line 300 shot misses further than a 10 degree off line 200 yard shot. One of the flaws of that argument (as proven by the Broadie stats recently referenced on the PGA tour site) is that that degree of mis-hit rarely goes over 225 yards, so what's the point? You are providing fairway for shots that will never see them.
Also, as TD notes, the differential has grown. Tour players routinely expect their shots to stay within 10 degrees total (5 per side, or 4-6 depending on shot pattern, maybe) where as ams are closer to 20 degree total for 50% of shots, and 19-20 degrees dispersion for all shots (actually 19 degrees left, 23 degrees right)
Add in fairway maintenance costs (where the differential between FW and rough maintenance costs has grown about as much as the accuracy differential) and wider fairways that far out begin making even less sense today.
Again, for historical perspective, when Mac and Tillie wrote all those great marketing quotes (face it, their books were marketing tools) it was in the 20's. By the 30's, they had changed their tune in many respects. Right now is more like the 30's than 20's and that would factor in to making any design decision we make right now. We should be looking at Tillie's PGA reports for guidance, now, and maybe nearly forever, except at the highest end courses.