Why? I find it absolutely horrendous personally and would avoid any webpage that used it (got to the end of the presentation on my second try as I literally rage quit the first time).
Some reasons as to why I severely dislike it:
1) When it scrolls the background changes color. There's multiple transitions going on. It's sort of like going to a different website. I lose my entire concentration and interest.
2) No scroll bar. I can't get to the final slide without painfully going slide by slide.
3) When scrolling with the mouse, I lose control of the webpage for about a second. I can keep spinning the mouse wheel but nothing is happening. It's infuriating.
I should have clarified what I meant by "sites like this". I was referring to sites which have multiple pages that are presented as a scrollable single page. Without a way to jump pages at proper page boundaries it becomes a pain to read through them. I still hope that this becomes the norm for scrolling through sites like this one.