It's not really "iris" that is associated with makeup, it's orris root. Not all iris fragrances are based on orris root. When an actual orris note is used in perfumery, synthetics are usually used, since pure orris absolute, orris butter, or orris concrete, are some of the most expensive perfume materials in existence. But to add to confusion, often the name "iris" will be used in a pyramid when "orris" is the actual note.
An iris note, on the other hand, is often based on the scent of the iris flower, and is built up using aroma chemicals in order to reproduce the scent of irises without ever really smelling much like orris root. Orris root doesn't really smell much like iris IMO. Actually, it smells more like violets if anything. Orris root has has a very distinct smell on its own. The rhizome itself is not prohibitively expensive, and in it's powdered form it has been used extensively in cosmetics, and as a fixative in potpourri mixtures for many years. The yield of essential oil is very low however and it is difficult to produce, thus making natural orris perfume materials expensive.
I really believe it is the orris root note in DH that is giving people the association with "lipstick." Just because a fragrance contains an orris note however, doesn't meant that fragrance will smell like makeup, but DH is built around an orris note, rather than just containing this note.
Also, it is important to remember that natural orris root is one of the most common and pervasive allergens in both perfumery and cosmetics and thus is being used less and less due to this fact. (Whenever I had to work with the stuff, I had to wear a mask and gloves and still would be sick for days afterwards). The synthetic scent of orris root will often be added to cosmetics to smell like "makeup" even though there is no longer any actual orris root being used in the manufacturing of the product itself.