Rob Horwitz, who is co-founder of Directions on Microsoft and a former colleague of Muglia at Microsoft, called the departure a surprise but did note Muglia's long tenure at the company. "He has been there 23 years, and there could be some element of burnout or just wanting to work in a different environment," said Horwitz.

"In general, I think Muglia's done an amazing job," Horwitz said. Muglia has had to deal with possible conflicts like pushing cloud computing, which is about getting users off of on-premise systems, and promoting Microsoft's systems management tools, which are about managing on-premise systems, Horwitz said. "I could see a big challenge to how do you grow both those businesses when they're pulling in different directions," he said.

Muglia's departure could be related to an internal competition for grooming of successors, said analyst Al Hilwa of IDC. "That always leads to people leaving, depending on the way the winds are blowing," he said. "Microsoft is a big company. They look up to big companies like GE or IBM, for example," from a management perspective, said Hilwa. Those companies develop succession strategies early, he said. "I think it may be Ballmer prefers to bring in someone from the outside versus somebody from the inside," to groom as a successor down the road," Hilwa said. He also cited the departure of Ozzie and the shift to cloud computing from Ozzie to Muglia as possibly creating internal tensions. Hilwa doubted Silverlight was a factor in Muglia's leaving.  

But for customers, management changes just mean the "show goes on," Hilwa said. "At the end of the day, they don't matter to customers much," he said.