They weren't officially released though, I think it was fans who came up with the stems themselves from what I remember.
Guitar Hero/Rock Band stems =/= official instrumentals. The mixing on those is COMPLETELY different when you put the stems together. Even if you count those, there's still no instrumental of any of the interludes (the ones with vocals/speeches, anyway). The only songs with official instrumentals are Iridescent (which wasn't released by the band, it just randomly appeared on Youtube) and Robot Boy (which fades out before the song's over anyway).
I had the original upload bookmarked, it appears it's been taken down (the one Malvar posted is real, but not particularly good quality). The guy who put it up claimed to have official instrumentals of all of A Thousand Suns, even made it a point in the video description to say things like "I'm tired of all the crappy fake instrumentals out there, here's the official one." He never uploaded anything else though, said he was only willing to trade for an instrumental version of an album by some band I've never heard of.
I don't get why the people that make remixes/mashups of certain songs don't also release the instrumentals and/or acapellas for them when they can't be found anywhere on the internet? I mean for example, if you've made a remix with your own instrumentals and are using the original vocals would it still be difficult to separate the two to extract the acapella?
-_- For example, if someone made a remix for "When They Come For Me", which consists of the original vocals from the song laid over their own instrumental track, wouldn't they have managed to extract the acapella of WTCFM in the process of making such a remix? If so then why don't they release that acapella cause there are hardly any WTCFM acapellas to be found online.
If you have resources that no-one else does but which everyone badly wants, you have exclusivity and you have control. And, in some cases, you might have gotten these resources from an associate who will continue to supply you with more exclusives provided that you can be trusted not to leak things.