I can probably find out more of course, but at this time I only know (for a fact) that there is "glue" in there. DisplayPort is a packet-based system while DVI is serial, which I suppose has something to do with adapter price. What's going on specifically in the dual-link $99 product however is a bit of a mystery. It may even have something to do with DRM (DHCP vs HDCP).

The adapter is supposed to work with all Dual-Link displays, not just Apple's 30" - however it requires Mac OS 10.5.6 and is specifically designed for Macs. So when other computers come out with mini DisplayPort connectors, this adapter will likely not be suitable.

Incidentally, Apple's adapter prices seem to be the lowest around. Every other adapter out there (for straight up DVI) looks like it was made of random (but suitable) parts and costs at least $3 more.