US airlines use the same pricing strategies by flights so differences are the same as here, but tend to allow same day standby for free to their elites and passengers booked in C/F.

The main element here is that they all do it, so it is not so much a question of whether the policy is profitable as such, but that if one airline stopped offering it, it would typically offer a competitive advantage to its competitors. To a large extent, the US majors "match" each other even more than European ones including typically having the exact same fares on given city pairs.

It is also worth noting that increasingly, US majors are now introducing "basic" economy fares which are stripped of some usually available US airlines economy perks (e.g. not upgradeable). I'm not sure if they also lose same day standby but I'm sure that some posters will!