It isnt about integrity. When your that famous and respected you have enough reputation to burn. He wanted to do something new and fun. I definitely thought it was funny
It may have also been a chas grab, but the guys net worth is at almost $50 million at this point. Also, Mike Stipe of R.E.M. did a commercial for some shoe company in the early 00s.
Dave Grohl of Foo Fighters did a spoof advert for Scissor Sisters about 2 years ago. Just food for thought.