Stressful events in twos or threes (or more?)

They say that some of the most stressful events in life include (in no particular order): getting married, having a baby, buying a house, selling a house, moving, changing jobs, work (needs no explanation). That said, I'm wondering why I/we have been prone to endure 2 or more of these high-stress periods in each of the last few years. Just to recap:

2003: get married, get laid off, sell house, move cross country, new job
2004: buy house, move (local), survive startup hell
2005: have baby, change jobs to escape startup hell
2006: survive work
2007: have baby, survive work, sell house, buy house, move (local)

To be fair, we've really been blessed in terms of selling our house in 2 weeks in a down market, and finding a wonderful new house (and not getting outbid on it!). Still, things will be so much more calm when the smoke clears and the move is done.