This is true. However, there is a difference between, "I'd like to spend more time with my family," which is, as you say, kind of a generic excuse, and, "I want to rebuild my relationship with my estranged wife," which is a lot more personal and displays a level of vulnerability. Add to that the insider comments on the touchingness of the memo and I think it's unlikely that this was the typical generic excuse.
CEOs always say they want to spend more time with their family when they step down. To me, it seems like good timing for the CEO of a real estate company to step down before the current meltdown.