It would be interesting to see how that compares with other professions. Do carpenters or dentists leave for other fields at the same rate? How about other types of engineers?
Of course, once the Great Recession hit, myself and many others that I graduated with either left the profession for other employment or simply never found jobs to begin with (that was me). Luckily I was already programming in grad school, and what was something I was filling my time with while looking for an architecture job became a new profession and I never looked back. Given all the comparative benefits of Software Engineering over Architecture, it's been a good move for me.