I'd argue that GTA 4 is a mediocre port-could have been done a lot better but there is really nothing specific in relation to porting to complain about (no horrible lag, controls aren't a mess, etc.).
Of coarse they did anyone investing money in anything always would like a profit. There is no excuse for Saints Row 2 to run so crappy hence, Saints Row 2 is a horrible port. You can't be upset for a company putting out a fantastic product then saying they invested money in it. If Rockstar released GTA targeted at a low age group and removed anything horrible, no matter how much they invested and how polished it was, it would flop. You will find some good ones out there, but your majority of gamers, especially gamers with a source of income aren't 7. You will not find many very succesful games targeted at a '7+' audience. The game you mentioned is far different than anything in the GTA like category.
As you say trial and error are how you find out what people want, and the GTA series has had much more time with that than these others have, giving them a bit of an advantage. So it seems your upset they haven't flopped and other games that have taken the GTA style of play just havent lifted off. They put alot of time into this game, yes it could flop, but they have made a good reputation for themselves by not allowing that to happen with their other products. A good game, and good research into what people want is as good as mind reading. Because from what you had said it made it sound like you were angry that GTA gives people what they want. You might want to go more into detail about a gold digger series then.