New York, NY
Im not sure how Apple does things but the monitor isnt really the focus here. I suspect that Apple Thunderbolt displays simply use DisplayPort at the end of the chain internally and supports a host of other features off of the Thunderbolt connection (USB, audio and so on). Its my Understanding that Apple Thunderbolt monitors require a Thunderbolt connection to work at all though so a DsiplayPort port wont cut it.
The focus here though is that Intel has an Intel video subsystem hardware requirement in the spec for Thunderbolt. This is why higher-end solutions like LGA2011 / X79 motherboards dont have Thunderbolt support (since they have no built in Intel video subsystem) and why some comparatively lower-end LGA1155 / Z77 solutions do. Apparently with the use of software you can drive a display through the Thunderbolt port using a discrete video solution (AMD, nVidia and so on). This may be how Apple does it but Im not sure. Apparently Intel is very particular about how this is done though and any solution like a hardware solution that bypass the built in Intel video subsystem or could bypass it in hardware is denied certification. Im not 100% sure on this but that was my understanding.
An example of this would be the aforementioned ASUS ThunderboltEX card that never made it to market presumably due to the lack of said certification (based on a presumed hardware bypass).
So for example, since its very likely that the Apple Mac Pro refresh in 2013 will be based on something like Intel Sandy Bridge-E or (more likely) the Intel Ivy Bridge-E LGA2011 / X79 / C606 platform then there most likely will be no Thunderbolt support.