For alien vs Predator :
i don't think they have pushed tesselation as far as the demo of Uningine , it's lightely used perhaps and only on PC i assume ! Not sure PS3 and 360 can do it ??
And for a multiplatform game i have some doubts, but perhaps it's done on PC ?

For UnlimitedDetail , it's some advanced Voxel Engine in fact :
What CPU, memory, and graphic card is necessary to run it ?
Not sure it could run on a today standard hardware ?
And like it's said, it don't work for animations, only static geometry !
A game like Bad Company 2 with destruction environnemnt features or a game using physics couldn't use it !
Instead Tesselation could run it , caus i's a process running in top of standard polygons having a texture (just rewatch the first video )!

I think tesselation will be the next step and you can run it with a DX11 card already available !

The think i see , is that tesselation seems to bring some texture deformations, on some objects like the dragon it's ok , but on stones, that's visible.Perhaps you will not pay attention during gameplay !

texture defromation of stones

okay it's not very visible also ,and it happens caus tesselation is adding polygons on a flat polygon and textures.