That is very true. The smoking kills all the capillaries (small blood vessels) in the gums and the gums lose their source of nourishment.
Smokers gums sometimes fool you to look like they're healthy because they don't bleed but it's only because they are starved of nourishment.
(you can believe me, I'm a dentist)
Is that the same as, "you can trust me, I'm a doctor"? ;^)
FWIW for the health/lifestyle nazi's who want to "not hire" smokers because of the burden on insurance rates: It is MUCH better to be a thin smoker than a fat nonsmoker. Diabetes is epidemic among the obese/fat and drains medical resources. It makes more sense to not hire fat non-exercizing persons.