I don't know how much more retail rental prices are but I haven't seen prices of products be higher at station stores. I can only guess, part of it might be culture and part of it might be there's so much competition. If you won't sell at a good prices the stand next to you will or the store just outside?

As for culture, maybe this is also competition but I've always been surprised that vending machines in Japanese hotels cost the same or not more than say 10 cents more than the convenience stores outside. A soda 500ml soda at the vending machine in the hotel is say $1.30 which is the same price at 7/11 or the vending machines outside. Where as in the USA, that same vending machine in the hotel would sell the same soda for $5-$8

I can only guess it's because there's a convenience store usually within a 2 minute walk of most hotels, open 24/7, and they're usually a relatively pleasant walk (vs walking across a huge stroad and giant parking lots like much of the USA). Still, the vending machine is more convenient so I'd expect a price hike but given I don't see one I suspect culture has something to do with it too?

AFAIK, there's nothing legally preventing stores from charging more at more-convenient locations. However, in practice I don't normally see it. I believe (not sure) that major convenience store chains, for instance, have fixed prices for the same reason Walmart does: it's too much trouble to track different prices at different locations. As for restaurants and stuff like that, there's usually a lot of competition, so I just don't normally see obviously-higher prices at locations in stations or airports. Of course, some things are obviously more expensive than alternatives: milk at a convenience store is more expensive than almost any grocery store, for instance, though usually not by much. But for whatever reason, I just don't see such obviously and ridiculously jacked-up prices as I see, for instance, in American airports.