TJ’s may be lower margin on what they carry than Safeway would be on comparable items; they achieve that by avoiding carrying lots of the low-margin items every other grocery store spends lots of money devoting floor space to.

(But those are things people tend to also need a lot, so TJ’s ends up being an extra shopping trip, instead of a replacement.)

I'm not convinced that the value is better. Most of the stuff at TJ's is reasonable quality, but the prices are often lower only because there's less product in the package. I'd have to sit down and compare unit prices before I could be assured you were getting a better value for your money.