Cartoonists getting vacation time is a fairly recent phenomenon; I seem to recall that it was led by cartoonists like Trudeau and Bill Watterson (Calvin and Hobbes), who had enough of a draw with fans to be able to force changes to the standard contracts.
I read the Chicago Tribune. What I find interesting is that, for some strips, when the cartoonist is on vacation, the Trib runs the "repeat' strips (that's what they're doing with Doonesbury this week). But, for other strips, they run an alternate strip in its place -- for the past few years, "On a Claire Day", which isn't a regular Trib strip, has regularly appeared as a replacement strip.
This week, the Trib has been running On a Claire Day in place of Get Fuzzy, but with the following note: "(At press time, new Get Fuzzy strips were unavailable. Please enjoy this strip in its absence.)" This is as opposed to the note that's running with the Doonesbury repeats: "(Doonesbury is on vacation this week. Please enjoy this strip from September 2008.)"
It seems to me that the Trib runs alternate strips for Get Fuzzy, with the "not available at press time" note, every couple of months. It makes me wonder / worry about Darby Conley.