How much money would iCloud on Android bring to Apple ? Probably losses in terms of millions.
At best it could only be a view only sort of thing since you couldn’t actually use it properly (android lacking all of the iCould functionality that iOS has). Apple has enough motive to develop iCloud for Android as it would have to develop iWork or iLife for other platforms.
It’s not comparable to iTunes since the only real commercial aspect of iCloud is the monthly storage aspect (iTunes match is a possible one, but that isn’t going to be useful for android since iTunes match is for iTunes). iTunes on the other hand was basically a way to get people to buy Apple hardware (iPods, iPhones, and iPads), and media content (music, movies, and apps). Far greater commercial potential.
I'm not clear how it would lose Apple money at all, but I could see some Android users being attracted to buying a Macbook/iMac if they knew they could access their files in their Android phone.
It’s not really a native usage situation though. iTunes for example, has no interaction with Android (or other phones) and Apple pretty much avoids supporting other mobile platforms as much as possible. There was a big deal a few years ago when Palm tried to fake out iTunes so that it would be recognized. Apple went out of their way to stop that and ensure that the only support was going to be iOS devices. There only Android development Apple is even doing is the Beats music app and that was solely because it was acquired. I bet that development of that app in general will have nothing to do with development of Mac stuff in general. It’s going to be it’s own corner.