Contrary to my initial suspicions, a similarly high proportion of GMs have also only been in place for fewer than three seasons. It is clear from the top end of the list below, however, that GMs tend to stick around a lot longer than the average coach.
I'd suggest this is understandable, since a change in GM usually signifies a wider shift in the direction of a franchise and wouldn't normally be used as a short-term fix to shake up a team's performance.
What is quite interesting is that several GMs have gone through three or more different coaches during their tenure. The list below shows the number of coaches (as at 26 November 2008) each GM has been responsible for _appointing_ (i.e. excluding any incumbent when the GM was hired) - this includes any interim coaches that lasted more than a few games.
This brings to mind a quote from a famous football manager in England (Brian Clough, for any native readers):
"If a chairman sacks the manager he initially appointed, he should go as well."(In North American terms, "If a GM fires the coach...")
So, there is certainly an argument that Messrs Waddell and Sather are lucky to still be in their jobs, given the relative lack of success they have presided over. Also seems unlikely that Dale Tallon would be given the opportunity to appoint a fourth coach with the heightened level of expectation in Chicago these days.
Post-script (2 February 2009)
Jim Rutherford has since hired a new coach (at the same time an old coach), as has Bryan Murray (now dangerously straying into Waddell/Sather territory). As widely expected, Brian Burke has also taken over from Cliff Fletcher in Toronto.
It would not be a surprise to see the GMs in Pittsburgh, Vancouver and Edmonton make their first coaching appointments at some point in 2009. Overall, though, the GMs still look to be much more secure in their posts than their coaching colleagues.
Post-post-script (27 May 2009)
Six more coaching departures (in Minnesota, Edmonton, Manhattan, Pittsburgh, Montreal and Calgary), only accompanied by a GM change in one (Minnesota), although Francois Giguere is also out in Colorado - with his coach seemingly a lame duck.