I think you've got a good point there, Moose. That's why I think you're most likely to get into jazz when you're still at that stage of life when you spend some time really sitting (or laying) down and listening closely to music; say roughly ages 15-25. After that, most people no longer have the time or inclination for that kind of close listening.
BTW, I noticed there was no room on the "gateways to jazz" list for people like Charlie Parker, Duke Ellington, Basie, Billie Holiday, Ella Fitzgerald, Horace Silver, Cannonball Adderly, Bill Evans, Louis Armstrong, Sonny Rollins, and so on. Helluva gateway!