I would first like to take the time to apologize for some of my colleagues on this site. Normally, this is a TERRIFIC site in which to get blackjack information.
I cannot seem to find the website you're talking about, so I couldn't verify that this is what they were saying, but those statements are not entirely accurate.
When the dealer has a six up, it's true that he'll bust 42% of the time, and he WILL make 19 or better about 31.5% of the time. But I don't know where the 8:13 figure or the 23% figure came from.
With a dealers' six upcard, and with correct basic strategy; your winning chances are about 3:2, which means you're going to win about 6 out of 10 decisions (counting a push as a non-decision), for an advantage of about 20%.
And what CP meant to say was that if you're STIFF you'll win 42% of the time. But in actuality there will enough times that you'll MAKE a hand & win, and this will bring the total win rate up to 60%.