Well, of course they are. But you can dip into the atmosphere at an angle, use it to change your inclination, then boost back to orbit (using the OMS in Shuttles case). Sure, you need to do it just right to not loose too much speed or even burn up due to overheating.
But if you could pull it off (and Soviets apparently beleived it was possible) you have an unique capability not really available to regular satellites l, where low orbit quick plane changes are basically impossible with any realistically available delta-v.
But if you could pull it off (and Soviets apparently beleived it was possible) you have an unique capability not really available to regular satellites l, where low orbit quick plane changes are basically impossible with any realistically available delta-v.