The first generation Iris devices used a proprietary Zigbee protocol which could not be moved to other controllers. But the second-generation Iris Zigbee devices (in the purple boxes) use the standard zigbee home automation profile (ZHA) and can be used with other controllers.
In fact many people with SmartThings hubs do use the iris second generation contact and motion sensors.
And Zwave devices, such as those from GoControl or Aeon, could always be used with other zwave controllers.
SmartThings only uses third-party certified protocols for its branded sensors, specifically ZHA. But that still may not be enough.
The Zigbee Issue
The problem is that Zigbee is still somewhat less portable then Z wave since each device has a “fingerprint” that may not be recognized by another coordinator.
Since you mentioned wink specifically, I don’t think the SmartThings-branded sensors work with the wink hub. Someone can correct me if I’m wrong.
Because SmartThings allows users to create their own “device handlers” (this is like a printer driver, it enables the SmartThings hub to set up commands into the format that the device expects), as long as the device uses the ZHA protocol, community members can usually help create a device handler that will be able to send commands to it.
but there are other zigbee coordinators, and I believe this is true of wink, which don’t allow users to create their own device handlers. So unless there is an officially-created device handler for that specific device’s fingerprint, you may be able to pair it to the network, but it won’t necessarily understand commands sent to it.
But the issue isn’t the SmartThings sensor: it’s the wink hub. The sensor is using a standard protocol.
So it really comes down to the specific alternatives you might be considering. At the present time, using Zwave devices will give you the most choices in terms of hub alternatives.
It’s still true that not all zwave device features will be supported by all hubs, but you should get basic functionality with any of them. Zigbee just requires more tweaking, and not all hubs allow users to do that kind of customization.