why is it that tricare can charge additional money for young adult dependents?

No, that's not what the Affordable Care Act says. The insurer must continue to offer you coverage, not keep you on your parent's plan for free. Family plans cost more than non-family plans.

Note There is one temporary exception: Until 2014, “grandfathered” group plans do not have to offer dependent coverage up to age 26 if a young adult is eligible for group coverage outside their parent’s plan.

You are eligible for group coverage through the military.

I had the same problem. We thought that Tricare included dental, went to the base dental office when I had an infected tooth, only to find out that they could only give me pain medication. Firstly, you have to sign up for dental under United Concordia, which is separate from Tricare. Secondly, the base dental office is just for the active duty military member. Dependents will only be seen under emergencies, in which case they provide a quick fix until you're able to get to a dentist off base. Even then, United Concordia doesn't pay for all the work, only a percentage. I didn't have to pay a copay, but I did have to pay around $400 for two teeth extractions and a deep cleaning. : )

No, the provision does not say it is free to be covered by your parents plan. They have to pay for you. They allow you to do that rather than find your own insurance because it is cheaper. You are over 19, the previous age at which children were dropped. If you think $2000 a year is high for your coverage, go and find an individual policy on your own. They must have a more comprehensive plan that costs more than the average health plan.