On a recent Friday night at Arthur's Tavern-a tiny wood-paneled bar on Grove Street, in the West Village, next to the piano bar Marie's Crisis-just a couple tables were occupied at 9:45 p.m., when a jazz quartet led by a young Japanese woman named Eri Yamamoto was finishing up its set. At Arthur's Tavern, which opened in 1937, there is no cover, but there is a two-drink minimum per set, payable in cash.