Looking at a couple of city pairs identified in the thread, JFK-MAD and ORD-FRA, I (with ITA Software) can't find business fares just $500 r/t more than cheapest coach, even when looking with 60-day adv purchase and variable length of stay, 5-10 nights.

Feb itins JFK-MAD on AA, non-stop:

cheapest business, $1989
cheapest coach, $827

Feb itins ORD-FRA on AA, 1-stop:

cheapest business, $2455
cheapest coach, $1040