Spokker, the site is called Theme Park Review. The tours are basically theme park tours and that's what you get. If you want to see and do non-theme park stuff you're free to add time before or after the official trip. With 50 or 100 people on the trip I don't think it would be possible to organise sightseeing trips that would please everyone. People who go on these trips like rides - by limiting the trips to theme parks, people are getting what they paid for and aren't paying for superfluous stuff they're not interested in.
Yes, these trips are fairly hard work in that the days are long and when the weather's hot can be fairly tiring. However, compared with trying to organise similar trips for yourself I'd call them stress free. The only concern I had throughout the whole midwest trip was making sure I made the bus! As larrygator mentioned, doing it yourself might involve driving on the wrong side of the road (or at least with different laws), navigating etc and, for the European trip, dealing with multiple languages. This is the sort of stuff that can make holidays stressful.
Personally, I don't know if Robb and Elissa make any money on these trips (and I have no interest in knowing - it's none of my business) but they certainly deserve to considering the effort put into them. You simply have to look at the cost and make a call as to whether it's value for money from your perspective.