There are a few places in AppKit where you need to determine an object's state by catching an exception because there's no method available. (Checking whether an NSColor is a pattern comes to mind -- only way is to try getting the pattern image and it will throw if it's not a pattern color.)

The really frustrating thing is that Obj-C didn't even have exceptions originally, so someone basically looked at exceptions when they were added and thought: "I know, I'll use them as part of the API"...