Jeff Stoltman, Wayne State marketing professor, is quoted in a story about Cadillac ending its 71-year national advertising relationship with Leo Burnett Detroit, a Troy-based ad agency. While General Motors Corp. has relieved Leo Burnett of some creative work months ago, the agency will still handle GM's Pontiac brand, as well as their service and parts operations. Many industry experts have speculated that Cadillac's decision came as a result of lukewarm reaction to Leo Burnett's Super Bowl XL ad for the Cadillac Escalade SUV. "It's clear that the agency-client relationship had been under duress for some time," Stoltman said. "That spot couldn't have been the last straw."