Correct, larger plans get it factored into the overall costs and hidden from you. When my company grew in size and we switched plans, suddenly I got dental as well for free (I had previously denied it cause I did the math). It may not even be something your employer pays for as it might be a perk added in by the insurance company. Depending on what the coverage actually is, it still may or may not be worth it. Hard to say... it is all so nebulous and poorly defined.
Always read the small print though...