“It is with mixed feelings that I am leaving AMD,” said Orton. “I am very optimistic about AMD’s future. I believe strongly in the strategies that brought AMD and ATI together and the talented employees of the ‘new AMD’ who are committed to winning in the market by delivering the best possible solutions for customers.”
They don't articulate on exactly why he is leaving, though it is never uncommon for upper management to leave or be replaced when a company is purchased by another.
To replace Mr. Orton, AMD will be appointing Adrian Hartog and Rick Bergman, who work in the consumer electronics group and graphics product group respectively. Likely, business will not be impacted by this departure. No more details were revealed from AMD.