Sean:
I've copied the GW rankings of Illinois and Michigan public courses below. I think you're on to something regarding the Detroit v. Chicago comparison. The Illinois list has a high concentration of courses in the Chicagoland area, while the Michigan list contains very few courses from the regions near Detroit. I'm sure someone may come up with a theory based on socio-economic factors to explain the dichotomy, but that kind of analysis is beyond my pay grade. Maybe it just means that people from Detroit go elsewhere to play their golf, while Chicagoans stay local.
Illinois
1) Cog Hill (No) 4 Dubsdread), Lemont (m)
2) Highlands of Elgin, Elgin (m)
3) Eagle Ridge (The General), Galena (m)
4) The Glen Club, Glenview (m)
5) TPC at Deere Run, Silvis (m)
6) Weaver Ridge, Peoria (m)
7) Thunderhawk, Beach Park (m)
Bowes Creek, Elgin (m)
9) Pine Meadow, Mundelein (m)
10) Harborside International (Starboard), Chicago (m)
11) Cantigny, Wheaton (m)
12) Annbriar GC, Waterloo (m)
13) Stonewall Orchard GC, Grayslake (m)
14) Ravisloe CC, Homewood (c)*
15) Harborside International (Port), Chicago (m)
Michigan
1) Arcadia Bluffs, Arcadia (No) 29 m)
2) Greywalls at Marquette GC, Marquette (No. 81 m)
3) Forest Dunes, Roscommon (No) 87 m)
4) Tullymore, Stanwood (m)
5) Belvedere GC, Charlevoix (c)
6) Lakewood Shores Resort (Gailes), Oscoda (m)
7) Black Lake, Onaway (m)
TimberStone GC, Iron Mountain (m)
9) Black Forest at Wilderness Valley, Gaylord (m)
10) Treetops North (Smith), Gaylord (m)
11) Eagle Eye GC at Hawk Hollow, Bath (m)
12) Angels Crossing, Vicksburg (m)
13) Bay Harbor (Links/Quarry), Bay Harbor (m)
14) Sweetgrass, Harris (m)
15) True North, Harbor Springs (m)
16) University of Michigan GC, Ann Arbor (c)
17) Pilgrim’s Run, Pierson (m)
18) Treetops North (Fazio), Gaylord (m)
19) Orchards GC, Washington (m)
20) Mines GC, Grand Rapids (m)