The iPad was a massive step up from previous tablet efforts-- both with touch technology and software experience.
Certainly there is a timing and luck component to both of these.
But "mostly luck" - that's just wrong.
The problem was that Google Video was missing some critical features beyond the video player. It was harder to upload videos. It didn't get embedding until after YouTube, and then its embedded player had a clunkier, less-branded interface than YouTube's. It lacked the "related videos" sidebar that was the crucial feature that made YouTube take off. Google also couldn't put up the copyrighted content that YouTube often turned a blind eye too.
YouTube's actually a really good example of the better product winning. They understood their market and aggressively put out features that their early adopters wanted. It wasn't all that apparent to outsiders that the product was better, because the details don't register for them. (Personally, I didn't see what the big deal with YouTube was until 2007 or so.) But for the key early adopters, it was pretty clear which one was more fun to use.