Maybe even a subcultural difference. Certainly many young adults, especially in Britain, view regular binge drinking (perhaps even waking up not remembering exactly what happened the night before and whether or not sex was had with a person who sober it would not be a considered option) as normal because it is so common. But that does not mean that it is not still a serious problem to others in the UK.
Penny has been written all along, to my read, as a character with an alcohol problem, a character who drinks … a lot, a character who not infrequently binges, a character who views drinking even more as the natural response to difficult emotional situations (be they hers or others), a character who tries to get others to also drink in that manner, even slipping alcohol into the drinks of those who do not want any in order to get them drunk (the slutty Virgin Cuban Libres) … it is just a basic part of the character outline.
The question to me is not whether or not the character is written that way, but whether or not the writers are going to keep playing it as the simple gag (like Otis a host of other TV drunks), or if they will develop it as a plot line, and if the latter if they will handle it in a way that identifies her as having a problem and still be funny, or end up all After School Specially.
I am not so sure that they are up to the challenge of successfully mixing humor and pathos, honestly. This ep did make the character’s alcohol problem so blatant that even those who see regular binge drinking, waking up without remembering the previous night’s events, unclear if poor choice sex had or had not occurred, using Pyrex measuring cups to drink alone if all the glasses are dirty, slipping alcohol to those who don’t want any, as “not a problem”, are forced to recognize that the writers are meaning these things as part of a character with an alcohol problem. Where they go with that from here though, playing like Otis or dealing with it? I don’t know.
(I could see Penny and Raj both accusing the other of having a dependence on alcohol of sorts and goading each other in dealing with it. That could get rid of both getting very old gags at one time.)