I would agree Chrysler's approach in this case is partly motivated by revenues from trans fluid sales. But the company does put a significant effort into optimizing the fluid formulation and their transmissions designs to work together, as well as maintaining quality control over licensed production of the fluid. What LionelHutz notes above, about anyone being able to produce a trans fluid that is capable of meeting ATF+4 performance requirements, is basically correct. But they cannot publicly state that the fluid meets ATF+4 specifications/requirements without permission from Chrysler. This is a shrewd US marketing ploy by Chrysler, and regardless of what you or I may feel about the tactic, use of licensed ATF+4 fluid in certain Chrysler vehicles is definitely a warranty requirement.
Besides, it's not like legitimate ATF+4 trans fluid is hard to find. Here is a fairly current list of licensed ATF+4 trans fluid brands:
Advance Auto Parts ATF+4®
Amalie ATF+4®
Auto Extra ATF+4®
AutoZone ATF+4®
Carquest ATF+4®
Castrol ATF+4®
Castrol Transmax ATF+4®
Chevron ATF+4®
Citgo Transgard ATF+4®
Coastal ATF+4®
Craft+4 ATF+4®
Federated Auto Parts ATF+4®
Great Wall ATF+4®
Havoline ATF+4®
MAG 1 ATF+4®
Mobil ATF+4®
Mobil Super ATF+4®
Mopar ATF+4®
NAPA ATF+4®
Northland ATF+4®
O’Reilly ATF+4®
Parts Master ATF+4®
Parts Plus ATF+4®
Pennzoil ATF+4®
Petro-Canada ATF+4®
Proline ATF+4®
Pronto ATF+4®
Pure Guard ATF+4®
Quaker State ATF+4®
Rallye ATF+4®
Ravenol ATF+4®
Sinopec ATF+4®
Super Tech ATF+4®
Tutela Transmission Force4 ATF+4®
Valvoline ATF+4®
Value Tech ATF+4®
Wolf's Head ATF+4®
Xcel ATF+4®