Just because you haven't heard of it doesn't mean it isn't common. Parents take different approaches. I had some friends parents who preferred we did it in their house where they could maintain some level of safety than us drinking recklessly in field. Others thought providing some beers was better than us buying the cheapest vodka available. And I'm sure other parents wouldn't have liked this approach if they knew about it.

I'm familiar with the "semi-supervised drinking inside" approach. "Provide beer so they don't drink cheap vodka" isn't an approach I'd heard of; it's close enough to my Poe's-law straw position to weaken my argument.