Since you could trivially turn aac files into mp3 files in iTunes your quote:
"Sure you were free to get ANY other mp3 player in the world, as long as you were ok with losing all your music"
Is completely wrong. I can only assume you are one of the vast throngs of Apple haters who hate Apple and their products because it is trendy to hate trendy things.
I know the iPad supports pdf format, and I think also the epub format(?), which I believe is the big open standard that everyone 'should' be supporting? How is that bad evil and wrong? Apple has great adoption of standards for its web browsers (please don't complain about Flash, for starters it isn't a standard, for seconds its horrible, for thirds it is used mainly for adds which are also horrible, for fourths it violates usability and accessibility for fifths its one good use is dinky little free games, of which let me assure you I have it on good authority there are quite a few of those on the iOS). Apple is by no means perfect nor lily white, but to attack them on standards when they do so well in that area compared to most other companies is ... bizarre.
The only 'entertainment' companies that I can think of that do better at supporting a wide range of open formats are the small indie music and movie makers. Why doesn't Apple work with the indies to help them bring their content to a wider audience? That would be awesome. That you could legitimately complain about. But no, you pick something that Apple are actually good at to complain about. Why is it that when someone rants about Apple it is always opposites day???
The hilarious thing about your complaint is that all of the examples you give are obviously wrong, but there is a much better example: apps. Apps for iOS don't run on any other device.
...
The problem is, if you complained about that, you'd look silly, because as a general rule apps for one platform don't run on other platforms.
So anyway, to sum up the actual state of Apple 'lock-in':
(a) Open formats are supported on Apple products. (b) Some (e.g. music) closed formats are trivially easy to convert to open formats. (Turns out there are many converters for books that are cheap but not free, go figure) (c) iOS specific stuff is iOS specific (spot the tautology)
Would I prefer to be able to write apps for iOS in any language I wanted to? As a developer yes yes, OMG yes. As a consumer I would ask whether that means giving up the protections I currently enjoy.
What protections? Surely Apple's only purpose in life is to sell me sufficient numbers of these devices is to enslave my will to that of Skynet?
Not so! On my desktop I hardly download anything unless from a very highly trusted source. I especially distrust the free stuff. On the iOS devices I go wild and crazy, knowing that my private information is private, my data is safe.
So are you complaining about the walled garden? Why? There are a great many alternatives, none with gardens so nice. Leave the Apple lovers alone, the chains that bind them are so nice and shiny and make such pretty bracelets. Maybe if you're nice to them, one of them will bring you a drink of ice-water in your 'warm cosy place'.