While it's certainly true that many people make snap judgments which rob them of experiencing something they would enjoy, it's also true that many people are experienced enough and have enough self-knowledge that they can judge how something would play out.
Personally, at least since my mid-20s, I've been quite good at judging my own reactions ahead of time. I was perfectly right in how much I would enjoy 4e, Savage Worlds, and Legend, no more and no less, and I was quite right on how little I would enjoy other games, such as M:TG.
The thing is, I know very specifically what I like, and very specifically what I do not like, and what rules are required for those to come about, and I have more than enough experience to see whether or not that exists in the rules. It isn't especially difficult for someone to develop an ability to mentally simulate things - nobody here would have a problem figuring out what affect giving all wizards regeneration equal to their Int score would have, eh?
This is especially true for DMs, who have to deal with more of these rules than anyone else at the table, and who have to put the effort into fixing the problems that occur when rules don't get along well.