It isn't that nuanced; lactose intolerance is uncomfortable because there are microorganisms breaking down the lactose and releasing gas (and what not). Those studies are looking at whether bacteria that do not produce as much gas can colonize our digestive systems.

If the lactose passed through intact, it wouldn't be a problem. If enzymes weren't responsible for breaking down sucrose and there were bacteria doing it, HFCS would probably be even more popular.