I generally agree with jbcohen. However, I will say that any possible blame for readers treating ebooks as though it's a mature platform lies, in no small part, with the various boosters of the technology -- including the retailers ("our ebook service is great!"), reviewers and, uh, enthusiastic early adopters.
That said:
1) You can buy a tablet or computer, and use the apps to read books from different retailers.
2) Territorial restrictions are not going to go away. Sorry, they just aren't. There are too many contractual obligations and too many advantages to using local resources. What
will happen is....
3) As with most other format changes, the availability issues will be worked out, and this in turn will largely fix the problems caused by geo restrictions.
The thing is, when you are paying people to do the kind of grunt work to convert analog books into digital formats, you have to, y'know,
pay them. 
This naturally causes a bottleneck for the conversion process.
You also have contractual issues, for in many cases the electronic rights are not explicitly assigned or are otherwise in play.
Despite the fact that nowadays the average citizen of an industrialized nation apparently has the attention span and patience of a flea, and feels as entitled as the Sun King to have what they want at a moment's notice, and despite the promises that everything really does work perfectly with this wonderful new tech, it just takes time to work these things out.
Patience is still a virtue. I think. Let me check Wikipedia and get back to you.
