1. supply and demand -
a) if many people want to be brewers, there is a lot of competition, and this drives down wages. So I can hire the great brewer for a lower wage
b) Wine is "more exclusive and expensive". The wine buying customers have more money, and are less price sensitive to a price increase than beer drinkers, especially the guy who buys the case of cheap beer. Since the customers are wealthier, it may be beneficial to have more upscale sales people.
2 - product knowledge -
In general, there is greater wine variation than beer variation at a store. The beer customer doesnt know much, just goes and picks up something, anything. Maybe they will try a Stout. Maybe Porter. The grain bill isnt on the can. But for wine, the customer feels lost. They come in and ask "what goes with raw Kangaroo meat Sushi?" or "whats a nice dry Tan wine?". The higher end customer wants a sales person who can answer that.
Also, since wine costs more, and the owner must sink a greater cost into the inventory, they will tend to be more keen on turning over that inventory.