Okay, Microsoft’s Schedule + format predates the iCal “open standard”, so why is it Microsoft’s fault they’re not compatible?
It's Microsoft not being compatible with everybody else. Microsoft had the chance to jump on open standards during many upgrades of Exchange, even for mail. That's what Apple did.
If you are on iCal and Apple screws you over, migration to any other package using the same standards is easy. Not so for Exchange, you're locked-in, still paying dearly for those CALs.