Options are generally worse than just making the right decision up front.
They have a cognitive cost to users (try skimming the options in Seamonkey or Opera). They don’t solve the problem for the 90% of people who don’t look in the options. They increase code complexity. They increase testing burden and generally the non-default choice gets accidentally broken a lot.
Options are often a design cop-out. It’s better to make a firm decision.
Google Chrome Software Engineer Peter Kasting (pkasting), in a reddit IAmA thread where him and two other members of the Chrome team answered user questions. In an earlier comment, he explains how simplicity is maintained: “I don’t think people realize that simplicity comes from a willingness to say ‘no’ to a lot of requests. I’ve made a lot of people angry on the bug tracker by closing their bugs, but that’s an important part of what it takes. (Note, I’m not suggesting we should never listen to our users; I’m suggesting that tradeoffs are an inherent part of design.)”