The dealer is smoking you, I wonder what else is wrong with the car. They were never optional, I think the regulators would not allow it to be sold without them. I would guess your assumption is correct, I removed my center one just to get better vision, but MB made a storage slot. If the previous owner folded the seats a lot they can get in the way. Its like the roof bars, and the cargo cover, (standard) people take them off, and then forget.
They are probably hard to find unless you get lucky at a recycler!
The roof cross bars became an option in 01, but it is not a safety issue.