Look out in the next few months for companies that will disrupt classical client/server datacenter based storage with peer-to-peer protocols and in home devices (which don't have the same cost constraints that datacenters have). These product offering will in some ways be similar to dropbox, icloud, etc, but they will be an order of magnitude cheaper and an order of magnitude faster.
I work at one of these companies. http://spacemonkey.com/ If you're interested in P2P storage and distributed systems check us out, we're hiring.
First, that Microsoft or Apple are able to perfect these services, which so far they have not been able to do, and there is good reason that it may be impossible.
But assuming that it's good enough, you still need to commit entirely to one ecosystem. Certainly some people can do that, but some people can't, particularly as BYOD becomes more common in business.
This is the magic of Dropbox. They make a dead simple product, they make it available everywhere, but they don't overreach. So in the end you have something that's harder to use and can't get the novice adoption that Apple brings, but on the other hand, most people understand what a folder is these days, and what Dropbox does is conceptually several orders of magnitude easier than trying to figure out exactly how iCloud works and what edge cases are going bring about catastrophe.
The old "that's a feature not a product" line is clever, but it's been overused to death. I don't know the source of the quote, but I'm pretty sure it was originally to address the fact that a startup needs to have an asymmetric attack to succeed against large incumbents. If something can be trivially replicated then it can be copied by the large company and smothered simply by the marketing heft of the goliath. If on the other hand, the very nature of the product is something that has a parity mismatch with large companies, then they can not directly attack it. Dropbox has a bit of that because making a cross-platform service like that just isn't worth the money for an Apple or a Microsoft. It doesn't tie into their cash cows and it's not a big enough market by itself. Dropbox is not a direct competitor to them anyway, it's more of a symbiotic relationship, so who's going to kill them?
I don't know why you said that. Skydrive API at least are available to most popular platforms it seems.
iCloud is useless at work, and my officemate has switched from SkyDrive to Dropbox for the same reasons. We now both doubly benefit from the wide-ranging accessability and sharability of Dropbox.
Basically I don't see a difference between dropbox and skydrive (or gdrive or....) as a developer, if I had to choose, I'd probably choose a platform from a company that has a long history of building platforms (Microsoft or Google or any other big co) as opposed to dropbox which is a tiny startup somewhere with no viable long term life expectancy.
Given these why would I choose a neutral API?