Sadly, Windows is NOT a Unix like, and went on for ages lacking some of the most basic protections offered by a Unix like environment, and even today is still less secure by design. It was built up over the years to avoid paying to license a Unix like environment to build off of. (And it has been a very nice system to work with for the most part.)
Open or closed source, it doesn't matter. If I want to I can take apart a closed source program and look at what each and every command does. (This is how they can actually run on a computer, all those "zeros and ones" actually mean something.) Sure, it is a lot harder to read, is a lot slower, and generally a larger pain, but perfectly doable. Once I know how something works, I can break it. (On purpose. With computers and software it is extremely easy to 'break' things by accident as well.)
But the thing about an open source community? I'm not reliant on some company to get around to fixing some issue. I don't have to wait for some bean counter to decide that the company will save more money fixing the issue than settling the few lawsuits that come up or off set the losses in customer base because people lose faith in the product.
But flip the coin around and most major close sourced projects are backed by major finances and can afford to dedicate staff to fixing issues, rather than relying on a community of often part time volunteers to take a fancy to something and make it their pet project.
Open or Closed, they're all just as open to attack and errors, and there is no great difference in the greater scheme of things.
So really, iOS isn't closed and limited for your protection. It is closed and limited for the purpose of lining the coffers at Apple, to make their lives easier, and to limit what a competitor can do to take advantage of a wide range of decent projects.
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Flickr: Real-Luckless