Has it been confirmed that it is US regulatory labelling, or is that a theory?
I know of US products which come with a 110-20V adaptor (for example Kindle).
I had the same dilemma when I bought my Roku 18 months ago. Apparently the previous Roku adaptors were rated at 110-220V and had the same model number as the new adaptors, so the assumption was that the new adaptors are okay at 220V. My concern was that the manufacturer of the adaptor may have de-rated it due to problems at 220V. I tested my 110V adaptor at 220V and it worked, but I decided to buy a 220V adaptor instead. I didn't like the idea of adaptors bursting into flames

Mains voltages vary throughout South Africa and can be higher than 240V in some cases. If the adaptor is not properly designed then it is possible for some people to have no problems and others to have problems.
Okay, it is unlikely to burst into flames. It would probably have a thermal fuse which would pop and the adaptor would quietly die, but it could take the Roku with it.
This is just my opinion, maybe I'm being over cautious?