I keep my elbows tucked in,pretty much, and tend to knit socks on lines that I know are packed. I think I've been elbow-poked more poked by people using their iPads than I've elbow-poked anyone. But yeah, it could well be that they figure it's going to degenerate into "elbows out" so they tend to back off. Which also might explain why they don't when crochet is involved.