You can tell if that's the problem if you hold down the button and plug the headset in and they're recognised a plain headphones.

The N9 does indeed use the "standards body that no-one listened to" standard whereas iPhones, thus most 3rd party headsets, thus most Androids, thus Lumias use the "Apple did it this way so we'd best make it work" standard.

So to make an iPhone headset work on the N9 you'll need to buy or make an adaptor.