There is a reason why so few sites scroll horizontally and that is simple ergonomics. When reading, we prefer narrow, long pages. Hence books are the way they, hence the vast majority of website have a limited width, hence we have PgUp/PgDn keys and not PgAcross keys.
I had a look at a few of those sites, and they were all as awkward to view as expected; the massiveblack one actually scrolled vertically for me - have they learned their lesson already, or a quirk of my UA?
Ironically, there is a current fad for widescreen TVs/monitors. They are good for certain types of gaming but actually fly against the ergonomic grain for many other purposes. Obvious not designed for ergonomics, but more for economics; widescreen films came about because it was easier, safer and cheaper to build build wider cinemas (rather than taller cinemas) in the quest to squeeze in more punters.