BMW doesn't care about the tires so long as you put the same type back on, and the tread depth is where it's supposed to be. Since the M3's don't have run flats the most common problem isn't a concern.
The dealerships say that because your lease return most likely will end up a CPO, and which if the tires are not proper spec the car will have to sell as it sits or tires need to be replaced to meet CPO standards.
The only time I've seen issue is if someone returns a vehicle with regular tires when the run flats were the original spec.
E92 M3 - Track Rental
F80 M3 - The groceries won't get themselves.
Mclaren MP4-12C - ATS Package
F85 X5M - Work Truck