It's beer in the show. I don't see why it wouldn't be beer in real life. Grant it, technically Butterbeer is supposed to be alcoholic but due to the target audience, it is not in real life.
Let's be honest here though, the Simpsons jumped the shark years ago. The target audience for something like this is definitely more for people who remember the show back in its heyday with fondness, who grew up with it, and are likely well beyond the legal drinking age at this point. I highly doubt the show is picking up new viewers in the young adult demographic these days. Family Guy and American Dad have that market cornered.