Sure, you can sometimes read your own codes or take it to a parts store that might try BUT at ANY shop, dealer or indy, the $$$ you're paying is a flat rate fee and is theoritically paying for more than reading codes, the tech should be going a tad further into any needed diagnostics, checking sensor readings, wiring, etc. For the most part, a code usually means 'bad part' BUT not always and that's why there's the 1 hour diagnostic fee. It's also not just cars, it's everything else in this world that requires an experienced, educated person to properly diagnose any problem (IE: computers, heating and AC equipment, plumbing systems, TVs, appliances, etc, etc).
The dealers have to charge more because they have higher overhead than the little guy at the corner but should then also have better service, or at least in theory. Yes, I know that people also have bad dealership experiences too so let's not go there.