Let me put it to you from the standpoint of any other industry:
Two people are in the same job. One has 10 years of experience, the other is fresh out of college. The person with the extra experience will generally have a higher salary than the new person even doing the same job. Why? It's experience on reserve should it be needed, it's being rewarded for the time you've put in, etc. And it's the same in the restaurant industry. Typically you won't get new servers at restaurants with higher tickets -- unless there's an employment crunch or the manager is an idiot. People who get hired for the restaurants like this tend to have more experience and know-how than the server you can find at your lower-end places. And as a result they make more on tips because their experience deserves it.
To clarify, let's imagine tipping wasn't the norm in the United States, and waiters made a salary. So you wouldn't add a tip to your bill anymore, but food prices would rise accordingly. At a lower-end restaurant, where salaries would be lower due to the hiring of servers with less experience, the rise in prices would be less. At a higher-end restaurant, with servers with more experience, salaries would be higher and food prices would rise higher than at the low-end place. It's the SAME THING as waiters getting a higher tip due to food costs at a more expensive restaurant.
Now you may get the same service...but you're more likely to get more professional, better timed service, with less flubs than at the restaurant where servers have more experience. Again, it's not a promise...anymore than engineer Bob with 10 years of experience necessarily being a better, smarter worker than 25 year old new engineer Betty. But it's more likely.
Also, how do you know your server didn't work harder at T-Rex? Perhaps lots of things went haywire behind the scenes with the kitchen, etc, another table gave her/him a lot of grief, he/she was oversat, but you NEVER KNEW IT. With a good server you won't, with a less experienced server, you will know pretty quickly. And are you honestly comparing a restaurant like T-Rex at DTD to your local Applebees? The servers at DTD T-Rex are going to deal with a lot more demand for turn-over, little room to breathe or make a mistake, people in "it's my vacation, make it happen!" mentality, and general cheapness from people who are already thinking about how much they've just spent on their vacation, are irritated at the higher prices charged at touristy restaurants, and looking for ways to stiff the servers as a result. It's called grace under pressure, and those with experience tend to roll with the punches better.
If that isn't enough, in short...you knew what it cost before you went in. If you don't want to pay the normal 15-20% tip because the place costs more, then by all means, go to Applebees instead.