I know, it was an easy shot, but there's an important difference.
The lockdown here is on *two* devices. You want a laptop or desktop you can do whatever you want with? There's the macbook, imac and mac pro for that. Want an expandable handheld appliance with a limited (albeit ever-expanding) functionality that'll have no hidden surprises? There's your iPad and iPhone.
You may as well criticise arcade machine makers for vetting all the roms you can put in their hardware. Or any of the console makers for vetting what's available for theirs. Or that kindle can't do anything but display books. Experience has shown them all, time and time again that as soon as you open up a platform to anyone and everyone, quality and reliability take a hit, not to mention susceptibility to attack. It's a specific product for a specific market and like the iPhone, will be hated by geeks everywhere, but loved by everyone else who want something that just works. Apple will likely do little to stop people jailbreaking these things, they'll just make it difficult enough that only determined people do it.