During his championship run he drew in almost every segment he was in significantly. Sure you can put this on feuding with Cena but he's never lost a significant amount of viewers in his reigns.
Also, Miz is a star. Not just a WWE star, he's a reality star. He can go on any talk show he wants. He has a ton of twitter followers, he's a celebrity. Miz is the most over heel in WWE, maybe Brock Lesnar is on par with him now. He drew this week in a segment which dominantly loses viewers, in a Brodus Clay squash match. What more evidence is there? The guy is a draw, people care about some cocky idiot like Miz getting the hell kicked out of him.
Santino is over, but he's not Miz over. Santino can still come out to very little reaction, he just gets huge pops when he wins, like Ryder does.