countering with the right cross is a common method in boxing/kickboxing.
notice that vernon white stupidly and amatureishly steps in with his face leading his hand rather than his hand leading his face. he demostartes horrible punching technique. also his nonpunching hand is around his waist.
What is wrong with Wing Chun people? You are so desperate to find someone that can apply it at the highest level, that the slightest thing that looks vaguely like it possibly might be, is Wing Chun. Dude if you watch Mohammed Ali in slow motion you might see him hit his opponent with a veritcal fist at some point in his career.
It Liddel was doing wing chun as you say, why was his elbow so far out of his centre line? why was his shoulder moving so much? He throw a natural instinctive punch which happened to be a vertical fist.
His footwork is like something simular, which reminds me of football (that is soccer to those that do not know what foot means) Lets all play soccer cause that will make us great fighters.