This is a good point, but when you buy an iPad you are giving up that choice, and you might not know it.
When I buy a car, at least I know I can change the oil myself should I choose to. I can also install a new battery, or listen to any radio station I want.
I don't mind Apple selling a locked-down device, as long as people are aware that's what they're getting. How many people do you think would buy a car whose manufacturer dictated what stations were allowed to play on the radio, and closed off the oil tank with a proprietary cap so that you had to take it to the manufacturer to have the oil changed? Probably not very many.
So the danger here is that manufacturers take advantage of the mass-market's lack of understanding and preys on their desires for a very powerful computing system that just works, pushing more and more investment towards more closed devices at the detriment of more open devices without most people even realizing how it's harming them.
When I was growing up, I played games. I thought they were neat. I wanted to make my own. I didn't have the tools to do it. I couldn't even easily acquire them -- mom, dad and my sister weren't going to allow the youngest family member to install Linux on the family computer, and we certainly didn't have the money to buy development tools. It doesn't matter if I could install a boot loader to dual boot -- I wasn't allowed to mess with it unless I wanted to be grounded for months.
I was allowed to dumpster dive for 386s though. And I was allowed to do whatever I wished to those computers.
As long as people are curious enough, there are no barriers. Hell, there are still cars designed in sheds (and sold to the public).