Yes, the large bottles are meant to be opened and poured into a glass and then left for the next person.

I wonder if there is some type of "off premise" alcohol licensing issue which makes them keep in the lounge?

I'd imagine it is also there to keep people eating appetizers like appetizers. Though most guests never cease to surprise me, i.e. the couple I saw last week at the NY Hilton lounge with 8 plates of appetizers between the two of them.