That doesn't mean that they don't work.
Salicylic acid in facial wash works to unclog pores. Glycolic acid works to remove the top layers of the skin. They're both products that are proven to work and aren't considered drugs. By the way the FDA's definition isn't as clear cut as you put it, supplements which do alter and definately change the body aren't even covered by the FDA.
Salicylic acid IS classified as an approved drug by the FDA. It is allowed to be used in products to a certain percentage. Look on the back of your products that contain Salicylic acid, you'll see that the label says "DRUG FACTS". Companies are allowed to use FDA approved drug ingredients without having to get their entire product approved.
A product/ingredient doesn't have to be approved by the FDA to work.... BUT, if it DOES work and the company has not received FDA approval to sell it, then the FDA has the right to pull the product from the shelves. Think about it.. do you really want companies to be selling products that change/alter your skin's structure without knowing that the product has gone through extensive safety testing by the FDA? Most companies do not want to go through the time (or have the money) to get new ingredients/products approved, so they will simply either sell products that contain drug ingreidents which have ALREADY received FDA approval (ie salicylic acid) OR they will sell 'cosmetic' products that dont' contain ANY proven active ingredients and make vague claims that their stuff "reduces the appearance of"... in other words, they have 3 options:
1) Develop & patent a new ingredient/product that actually works and have it approved by the FDA so it can be legally sold.
2) Use a proven ingredient that has already been approved by the FDA and include it in their product (benzoyl peroxide, salicylic acid, etc)
3) Use only dormant and ineffective ingredients and avoid going through the FDA approval hassle and then make vague claims to avoid being sued by the FTC.
That's the reality of skin care products. Unfortunately there is no FDA approved OTC (over-the-counter) ingredient for wrinkles. RetinA is a FDA approved drug for wrinkles, but its not allowed in OTC products, only prescription. That's why OTC anti-aging wrinkle creams are mostly all junk. Now in response to your point about supplements, just do a google search for the number of supplement products that the FDA has pulled. the FDA is cracking down on these products.