SPJ had a great deal of latitude at MSR Cambridge, he could probably work on almost whatever he wanted. The problem is MSFT is rife with bureaucracy and it is a constant fight to get anything done. MSFT in general and MSR Cambridge specifically has lost a lot of their best people over the last 10 years. AFAIK it is expected to get worse under Christopher Bishop. With the recent win in Excel Lambda it is as probably a good time as any to get out.