Of course it's ok. It's a free market. There are at least half a dozen different companies I know of producing e-book readers. What would preclude Apple from competing? They don't have a monopoly on publishing or any other conflict of interest. They are quite well known for producing good consumer electronics devices so it does seem like a natural market for them to enter. Amazon isn't exactly a saint either -- the Kindle is a DRM-ed closed platform just like Apple's product would likely be.

As far as Amazon's success goes I'd say they're in good shape to compete with Apple toe-to-toe in digital publishing / e-book readers. Their only limitation may be the inability to offer a richer platform. The Kindle is pretty limited to just an e-book reader with tie-ins to the Amazon store. Apple would likely offer a device with a color screen, full audio/video playback, almost certainly a third party App Store. That might be more appealing to a mainstream audience that wouldn't spend $250 for a device that is exclusively an e-book reader. Amazon could easily adopt Android and beef up the Kindle into more of a general purpose platform. Competition is good.

Well my major complaint is that everyone goes "Why doesn't the Kindle have colour or a touchscreen?" when the answer is: "Because it's e-ink and it's really pleasant on the eye, and is black and white because that's what it is, and it's not a touchscreen because it's not possible with e-ink". Basically, e-ink is far better than LCD's, so any device with an LCD is missing the whole point of the Kindle.

E-Ink is great for e-books but I suspect a lot of folks, the ones who rarely read books, would prefer e-magazines, e-comic books, e-manga and web content in which case a color screen is very important. There's plenty of room for both but I suspect the more casual, multi-pupose approach, will end up being a bigger market.

Sometimes it helps not to be the first mover. Apple wasn't that for mp3 players or smartphones. Amazon has made some mistakes and Kindle isn't perfect, so there Apple can learn a lot from them.

I think Apple will deliver something a bit different from Kindle, probably something that can deal easier with much wider media than just books. There could be also somekind of podcast equivalent of text, where you can subscribe to a piece of free or paid content, and where creators can provide that content without going through book publishers or without some exclusive deals.

This article isn't really about books though, it's more about daily/weekly publications such as newspapers and magazines that are desperately clamoring to find a profitable foothold in the world of bits and bytes.