It's nice to see that Gordon Brown will be making his own personal contribution in this time of flux by dispensing with old traditions which have lasted... oooh, since about 1999. Because, as we all know, Prime Ministers haven't campaigned in a by election since Uxbridge, Eddisbury, or Hamilton South.
It's up to each individual Prime Minister whether they want to campaign in a by election. There are quite a lot of by elections over the course of a Parliament (12 Westminster by elections since 2005), and I guess it's not feasible that they'd have time to come to them all. Most aren't even that close and the incumbent doesn't face much of a challenge. Perhaps a convention did grow up through this frequency - the BBC article on Uxbridge refers to a thirty year tradition of Prime Ministers not appearing at by elections, but internet links to back this up are a bit scarce previous to '97.
Things have changed dramatically in those thirty years. The reaction of the media to by elections can be incredible, and it's increasingly important for the parties to get a piece of the action. Why else would smaller parties bother with the expense of fielding candidates? I caught a wee bit of the 1964 General Election coverage on BBC Parliament the other day, and it's a world away from the media circus now surrounding elections.
The claim that Glenrothes is different has some merit. The Prime Minister's own constituency is next door; having lost Dunfermline and West Fife as recently as 2006, Mr Brown won't want to lose the constituency to his East. This is probably the most compelling reason for his appearance. Unlike Glasgow East, it is his back yard. Furthermore, it's a bit cruel but probably true that both the new Leader of Labour in the Scottish Parliament and Secretary of State for Scotland are still too anonymous to make any kind of impact on the good people of Fife.
While Glenrothes might be a campaign Gordon Brown can't shy away from, I wonder whether the suggestion in the Sunday Herald Editorial from during the Glasgow East campaign still stands, and what the implications will be this time around;
"He is being kept away from Glasgow, not because prime ministers don't do by-elections, but because this Prime Minister can't do elections.