It's not a ludicrous idea, but Apple keeps the OS tightly locked down, apps are only allowed to do what Apple says. This keeps the phone stable - I've never had an iPhone crash, but all my previous smartphones, and those of my friends and family (including WM5 and 6, Android 2.1 and 2.2, Bada, and Symbian), have. It also helps the battery to last longer. You'll also note there are no call firewall apps, one of the things I'd almost consider jail breaking for.