He has a lot of respect for the Undertaker so I don't think it's that surprising. A match with the Undertaker at Wrestlemania is about the biggest thing a wrestler can do in their career nowadays (at least since the streak has become important). I'd say the biggest matches of Edge, Orton and Batista's careers came against Undertaker at Wrestlemania. Shawn Michaels match with Undertaker at Wrestlemania 25 is a classic and might be remembered as one of the biggest and best of his career. Punk could very well be having the biggest match of his career against Undertaker in several weeks.