KSM was waterboarded 183 times . His case was unusual, but it explains why American prisons are widely admired by the wrong sort of people.
Why do I mention this? Because, under the DMCA, circumventing encryption can win an extended visit to a US prison . Even describing encryption circumvention is illegal for Americans; so posts on the topic are either naive or a minor form of civil disobedience. 
So, if you are an American, you should read no further. We can read Apple Store EPUB  files on iBooks.app, but not on a Mac  or a Win desktop.
If, however, you are a Mac user and a citizen of a civilized country, you can fix this. You can take advantage of Adobe's relatively weak ADEPT DRM , which means you can buy ePub formatted books from Google Play, Nook Store (for now, anyway), and Kobo, strip out the DRM, and use them with iBooks.app, BookReader for OS X, Adobe Digital Editions for Mac/Windows , and other eBook readers.
There may be other ways to strip DRM, but most of the appnetizens I know use Apprentice Alf's DeDRM plugin for Calibre, or his related DeDRM Application. Alas, I couldn't prove that DeDRM worked on my two purchased Google Play books -- they are both DRM free! I was able to download them  and display them in BookReader, iBooks.app, and Adobe Digital Edition. BookReader had character set issues with one of the ePubs, but both rendered correctly in Adobe Digital Edition and iBooks.app.
The next time I buy a DRMd book though, I'll get it from Google Play and test out DeDRM. With DeDRM and Google Play I'll have my EPUB books on iBooks.app and BookReader -- and I'll also be able to view them using Google's web interface to EPUB books. Not to mention Play Books.app!
PS. I keep my EPUB books in iTunes, so the simplest way to get at them from the Finder was to save a Spotlight search in iTunes Books folder for ".epub". From that view I can right click on a file to open in Adobe Digital Edition (when it doesn't crash, see below) or BookReader (preferred, though it has character set bugs).
 But stayed sane, and was thereby made immune to prosecution and execution. So bit of a trade-off.
 Many of us have wondered why Amazon put an eBook reader on the Mac but Apple didn't. I don't know, but my best guess is publishers wouldn't give Apple permission. Maybe they felt DRM bypass would be easier on a Mac than on an iPhone, which is probably true. On the other hand thesesame publishers traded their future to Amazon for a bucket of glass beads and published on the broken Adobe Digital Editions platform. I think they're simply dumb as rocks. Jobs must have despised them, which may explain some of the trouble he got Apple into. iBook is supposed to come to Mavericks, but it hasn't shown up in the beta releases so far. Note BookReader will display ePub fairly well, but not FairPlay DRMd ePub.
 Why is it weak? I suspect because many of the devices that use it can't be updated. So fixing the DRM would make all of these devices useless, and cut off new sales. Apple can fix FairPlay because its software gets updated. Nobody remembers that Apple couldn't update DRM on the Motorola ROKR, so those phones lost the ability to play new music.
 Technically it's all caps EPUB, but I'll go with ePub.
 Now Flash free! In my testing BookReader had character set issues with one of the Google Play books, but Adobe Digital Edition and iBooks for iPhone did fine.
 Go to Google Play, then to book page, then "How to Read' then eReaders and other devices - click Download EPUB.
 I loathe the DMCA, but, I admire the genius of FairPlay for movies and apps on iOS and OS X. If we didn't have DRM we wouldn't have a vibrant app market, and we wouldn't be able to sync movies around our devices. If iBooks were available for Mac and Windows I'd probably tolerate it for books as well -- but it still feels like the wrong model. Books last a lot longer than most apps. The revised DRM model for music, whereby buyer identification is embedded in an otherwise standard file, might be the right balance for books.
- Walmart DRM: and consumers still don't care? Walmart abandoned protected WMA support, trashing their customer's downloads. All five of them. 9/2008
- The limits to DRM: my new car stereo 3/2007. This wouldn't be a problem today -- we have iPhones everywhere now and they play the music. In any case music went relatively DRM "free", at the cost of a 30% price hike.
- Why Apple can't license Fair Play 2/2007. Same reason that Adobe ADEPT has been hacked.
- DRM means the vendor must own the hardware: lessons from iTunes and phones 9/2006: iTunes 7 DRM update meant Motorola ROKR couldn't play new tunes.
- SONY - "My God, what a fiasco" 11/2005: SONY's DRM fiasco beggared belief.
- Perverse consequences of 'digital rights management' - media centers don't work well 11/2005: I think AirPlay is still proprietary?
- Where now for the iOS Borders eBook reader? 2/2011 - Kobo still sells ePub books!
- iCloud, iOS, and identity3/12 - still unsolved.
Update 7/13/13: I dragged about a dozen ePub files onto Adobe Digital Edition and it crashed. On launch. Forever.. Deleting its preference file didn't help, but I found a Digital Editions folder in my Documents folder. Emptying that fixed the crashes. Adobe stupid.
Update 8/31/2013: Just go Kindle and forget iBook
I wrote a subsequent post on Using Calibre and DeDRM Plug-In to remove Adobe DRM from Google Play .ascm ePUB files. I was able to get the process to work, but at the end of the day I realized I'd gone a long way down a dead end road.
Apple (and/or Apple's publisher partners) blew it when they failed to get "iBook" (FairPlay ePUB) support out for OS X and Windows -- not to mention Android. That was a game changing failure in more ways than most of us realized at the time.
Amazon has won this war. They own the eBook world. I should have bought a Kindle.