There's information on the timing and the selection of his replacement. It leads a number of bloggers to conclude what this post claims: "buyouts, cutbacks didn't push Wilse into retirement."
Agreed - no one pushed or forced Jim out, but I think he could have worked much longer if the past year wasn't so painful or the upcoming one looked to be one that allowed an editor to concentrate on journalism, not numbers. The fact that he helped select a replacement and lined up the journalism course to teach shows the plan has been in the works for awhile.
Willse told Editor & Publisher he always intended to stay for another year past the 2008 buyout cuts:
I think it's healthy for an editor not to stay too long at the party. Considering the economics of the business, it is a time to have a change in leadership."