It would be silly of Apple to drop the MAC requirement for iOS dev : lots of effort to port their tools on other OS with the risk of incompatibilities and they would loose sales too.
And there's no incentive to use Objective-C on any other platform, so with Apple pushing Obj-C on their platforms it makes sense to get a Mac for iOS development, particularly if you spill over to desktop development (which you can do in C++ of course).
I wouldn't be surprised if Apple someday has a Windows (or whatever) version of Xcode. That is, in a kind of parallel to the OP's essay, Xcode as we know it isn't necessarily "Mac-only" but simply built for Mac first.