They never said YouTube doesn't dominate video search. The accusation was “Google routinely displays YouTube results at the top of its search pages, even if YouTube is not the original source of that content.”
And, no, they don't.
They do dominate video search. But, would YouTube not dominate any video search? Hell, YouTube dominates Yahoo! video search.
It doesn't claim that YouTube doesn't dominate video search. Just that YouTube doesn't dominate when it's not the source.
Seriously, compare Google video search to Bing Video search, Yahoo video search, Duckduckgo video search, and see how YouTube links appear in the top results.
