One of the architects of Mac OS X -- and a top Steve Jobs lieutenant -- is out

"I've worked with Steve [Jobs] for 22 years and have had an incredible time developing products at both NeXT and Apple, but at this point, I want to focus less on products and more on science."

Spending more time with science, rather than one's family, is not the usual reason given for leaving a company where you spent the better part of your career. But that's what Bertrand Serlet says in the (AAPL) press release Wednesday that announced his departure.

Serlet also took the opportunity to praise Craig Federighi, who will be taking over as vice president of Mac software engineering.

But what does it mean? Early speculation among the writers who follow Apple like Kremlinologists studying the Politburo centers on the diminishing role of Mac OS X within Apple, its transformation (with Lion) into something more iOS-like, and the rising fortunes of Scott Forstall, senior VP of iOS software, who used to work for Serlet but is now perceived as outshining him.

Below: The paragraph we wrote about Serlet in June 2008, when he was considered a candidate -- albeit a long-shot -- to replace Steve Jobs. And below that, some Hacker News commentary on Serlet's contribution from two former Apple software engineers.

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