I'm a native Korean, Samsung Electronics employee for the last couple of years, although the following text does not represent my employer.
Actually the reason behind this seems to be twofold - health (you can't expect somebody who drunk heavily to perform adequately next day), cultural (Samsung isn't simply a Korean company anymore), and probably legal (the company is liable if drinking was part of the routine job, and it didn't do anything about it).
Decades ago, the only people working for Samsung (and probably most Korean companies) were mostly male Koreans aged somewhere around 30 to 50. (In the eighties, Korean women had a difficult time getting jobs on large corporates (except as secretaries or factory production workers) and were routinely fired for getting married) The only thing that they could do in common was drinking. Considering that Asian people have a blurry boundary between personal and professional issues, drinking (and for executives, playing glof) was a very essential task for successful working. Actually, companies even had "drinking VP"s who's job was to drink with business contacts every night, and nothing else.
Fast forward to 2012. Samsung now has some 300k employees, and more than half of those people are non-Koreans. Many employees have their spouse also working, which means somebody has to take care of their kids if they have to drink late. There are many non-Korean people everywhere, even on the Korean campuses. Business contacts are no longer limited to Asian countries. Suddenly, it doesn't make much sense to socialize by drinking heavily. You can't expect to be able to socialize with other people if they don't drink much, or don't drink at all.
The problem was that this "heavy drinking" thing was a sort of a "tradition". Many people, especially junior/senior management people who were working for Korean companies for decades, found themselves uncomfortable to socialize with other people without excessive soju or whisky or whatever. So, corporate policy kicks in, and tries to change the culture. Not only by simply banning "drinking", but by trying to suggest alternative methods (e.g., sports activities or doing charity work).