Don't they have to change it anyway before they can rent it out again?
They don't "have to." Depends on the quality of tenants and the amount of rent they want to charge and how desperate a tenant is for an apartment.
It's usually a good business decision to replace worn out carpet and paint before re-renting. In the long run it enhances the rent that can be charge especially in a desirable area.
However, understand that nothing depreciates to zero if it is still usable no matter how worn it is and you are responsible for damage that you cause. You may have to resign yourself to being dinged some for the damage. Make sure you photograph the place and the condition. If the owner charges you too much there is always small claims court.