I think what you're looking for is
on this page:
If requested by the customer, United can check strollers at the departure gate. United is not liable for damage to strollers. Customers cannot purchase excess valuation for strollers.
That is regarding gate-checked strollers, not (normally) checked strollers, which is what you posted. The result is the same, though, "not liable for damage".
I do not know if this policy is DOT compliant. I can only assume that it is as it is still listed on the web site roughly two years after the DOT notice you cited. You would have to contact the DOT, as has already been suggested, to know for sure.
I believe that the reason the airline does not want to assume liability for strollers is that strollers are rather easy to damage and are not well protected as is most luggage. I have seen passengers put their strollers in bags prior to gate-checking them which should help somewhat. I can't recall ever seeing a stroller returned to the jetbridge damaged though I'm sure it does happen.