The issue is that we don't have a full listing of who was showing what on what hardware and what resolution/vsync was used along with what the (realistic) target for xbone is. We have some which clearly have been caught using PC's in place of xbone (nothing was mentioned prior to the leaked pics) and others which are using devkits based on xbone.
Forza was nice, but in looking at other PC games, driving games seem to be the easiest to get decent bang/buck. Take a look at how well Dirt and NFS run on 7770. 60fps/1080p for the most part. So seeing Forza hitting roughly the same is par for the course.
Seeing BF4 hitting 1080p 60fps on xbone would be a bit more impressive. But that demo wasn’t running on xbone hardware. Right?
So as far as I can see, the only ones actually running on xbone hardware (spec) are Ryse, Forza, and KI (which looked like a xb360 game). The rest, I’d say it’s safe to assume they were running on pc’s without regard for spec (maybe realistically handicapped as you suggested, maybe not) until proven otherwise.
The motive for bringing high-spec pcs to show off xbone games is obvious. The reasoning for bringing more reasonably specced pc’s to represent xbone games is also obvious (big savings going with barebones amd bulldozer + 7770 over top of the line nvidia hardware and sandy/ivybridge)
We see what direction was chosen for xbone demo hardware (that we’ve seen) and until we see others which were a more fair representation of what to expect from xbone, I think it’s safe to assume the ones which were not photographed were likely running on non-spec hardware (aside from Ryse, KI, Forza).
It’s a moot point for now as the façade will be over as soon as the real hardware and games make their way to shelves later this year. Until then, take what “gameplay” you see of xbone software with a grain of salt.
The whole thing is funny to me though given the lack of interest by MS to bring a high-spec machine to market in xbone:
“Nobody would notice the difference, but let’s just use these uber workstations just in case they do!”
Why bother?