Does this mean that any strings I have in my program take the same amount of space in RAM and ROM?
Yes.
If so it seems rather inefficient use of resources.
How so? The strings have to be stored in ROM (Flash memory). After all, that is the only place that initialization data can be stored. The strings are, when the Arduino boots up, copied to SRAM, for ease of access and so you can overwrite parts of them, as needed.
You can prevent the copy to SRAM by wrapping the string in the F() macro.