Yes, most hosting companies charge much more for ram that it costs you in the store. Some of that is mark-up, to make a profit. And part of it is as a proxy. Since ram limits what you can do with your server, the more ram you want, the more you plan to do, and the more you are willing to pay. You see this a lot. ISPs charge more for extra IP addresses, not because they cost much, but because they are a sign you will be a higher-end user, and use more of other things that are harder to bill for.

A hosting company has mostly fixed costs and shares resources. So to decide how many people they can put on a machine, they need something, and RAM is a common choice.