I'll ask next time I'm in the stores and see what they say. I bet they make more money off extract while spending more time on all grain (which from a businiess perspective means they should be pushing extract).
Maybe they do, but I wouldn't bet on that.
I'm going to Northern Brewer in about a month, and I'll buy probably 4 sacks of grain, two wine kits, lots of yeast, and maybe some more kegerator supplies. I don't go in often (maybe twice a year?) but I stock up when I go in person. I also order a LOT of stuff online. I'd have to guess, but I'd say that I easily spend $750/year at Northern Brewer, and have yet to buy extract (or hops) from them. Actually, maybe I did buy some extract 6 years ago and I think I bought some hops from them last summer. But otherwise, it's "bigger" stuff like kegging gear, sacks of grain, even beer line. The last time I was there, I bought 50 feet of beer line.