My daughter checked a brand new TravelPro soft-sided bag last month that I'd given her as a birthday gift (nearly $400 on sale). First flight and the axle holding one set of the wheels arrived broken. Delta's response was to send her a brand new suitcase, but it was a hard sided Ricardo, which I'm sure cost much less. Luckily, we have a very good luggage repair shop near us, which many off the airlines have used for covered repairs, so she dropped the bag there to get the wheel replaced. The shop is an authorized location for Traveler warranty work, so they said they'd check with the manufacturer about covering the wheel replacement since the bag was brand new. Luckily, I think it's probably less than $50 if she has to pay out of pocket.
The same shop has replaced wheels for us after airline damage and the owner has encouraged us to keep using our old 2 wheeled TravelPro bags as long as we can, because "they don't make them like that any more." Only down side is that they are much heavier than most bags now, although we still manage to stay under the weight restrictions.
I suspect the 4-wheeled bags are more susceptible to wheel breakage than the 2 wheeled ones that offer ore protection.