@tanguatlay,
Yes, enclosure, as Dale mentioned, has something to do with it.
in a store/car/taxi/... and I'd also say that public transportation has something to do with it.
Contrex:
Quote:You can say 'in a bus' if you want. In general we can say we are on, or in, a public transport conveyance such as a bus, train boat, or plane as we choose,
I'll suggest that this isn't an "as we choose" issue. We use 'on' when we refer to the public transportation sense. We use 'in' when we refer to a specific situation, eg.
A: Where is Jack?
B: He's in/inside the bus.
Also "He's on the bus/ferry/ship/... .
And of course, as HH mentioned, there is an element of convention involved.