Its what I was told and that as a consequence those areas can sometimes need a touch up. I've read that as well.
Well I'm sorry but you've been told wrong.
As I said, tattoo ink is deposited in between the upper epidermis and the dermis. The only way you will damage a tattoo by rubbing is if you peel off the upper dermis, and you certainly wouldn't want to do that, that would be very painful and would certainly need a skin graft.
They only sure fire way of a tattoo going dull over the years is from too much sun which causes raised melanin in the skin which disperses the ink in minute amounts.
When you see dull tattoos, this is mainly due to the upper dermis being damaged or abrased and the sun, nothing to do with the tattoo fading due to rubbing.