People write FOR the platform the customer uses.
They write ON the platform they (or their employer) chooses.
If Macs are chosen by some companies whose customers use Windows you're writing on a Mac for Windows.
Apple would love that, it's been the other way around for decades :)
Personally I don't use a Mac though I might purchase a Mac laptop at some stage for photoprocessing.
We develop on Windows, deploy on a mix of Unix flavours as web applications. We could just replace the Windows boxes with Macs but why bother as they work well and are cheap (plus we DO sell them as well, we're a systems integrator and IBM reseller as well as creating software).
So we develop ON Windows FOR AIX (and SCO and Linux).