IMO, the only thing that kept Forstall at Apple for so long was his relationship with Steve. While I have no hard evidence, my hunch is that the relationship was beyond professional and made a hidden standard in Steve's world that was not well known.
A lot of corporate America is like that, while there are dozens to thousands of people that qualify for a position, the upper echelon of a company has a hidden standard to make that level. This is where the "right" school or "right" charity or "right" life philosophy comes into play. I know people that have hired PIs to dig into executives personal and political lives so one can position themselves of an executive post. In fact, I have been told European corporations are worst where they are straight-up saying you need to be a specific social class and schooling to even consider a position beyond that of a middle manager.
What that hidden standard between Scott and Steve was, I have no idea. When Steve passed away, my guess is those those hidden standards also went away. This is only conjecture but the executive guard that elevated with Apple's return to greatness may have viewed NeXT alumni as a liability. With the Apple Watch out and hitting the vanguard, who knows what is next.
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The "soul of Jobs" has been split between Ive with the design eye and Cook having the corporate shrewdness. It is nearly identical to what happened when Walt Disney died and two of his right hand men took the reigns.
Been told that Steve's Jobs office at the top floor of Infinity Loop One is under lock and key to this day with nothing changed from the day of his death with the exception of the occasional record search and archive of his iMac. That whole building will probably become a historic landmark and mothballed when the Mothership comes on line.