Do you expect that any non-Apple device will be able to use iCloud? Vendor Lock-in is what's important here, and it's definitely been made stronger by this move. Once all your data is in the cloud, do you want to go through all the effort of moving it to a different cloud (if you even can!) or do you want to cough up a few extra $100 to buy from Apple and make things easy.
Given that Apple is supporting Windows for Photo Stream and iTunes Match at least, I would say the answer is closer to yes than you are intimating here.
While they are in control of your data, you will be faced with a question every time you upgrade your hardware. Do you want to interact with your own documents and music using a clunky interface, or do you want to use an interface that makes you feel more in control and happier?
The above question is a little contrived, but I believe that it is fairly close to the truth, Apple has always been a company based on making you feel good.
Apple support Windows because there would be an uproar if Windows users bought iPods and iPhones and couldn't use them. They do the bare minimum they have to however.