I know, reading the other comments in this thread, that I'm going to receive down votes and lots of disagreement for this, but I'm with Cameron on this one.
I think to have the debates in April would make every news story about the debates. It was the Green Party conference today, and far less time has been given to their policy announcements than should have been due to this ongoing stupidity. The closer the debates are to the election itself, the dumber the coverage will be, and the less it becomes about what they're saying and more about how it looks.
Also, isn't the thing that we vote for our local MP, not the guy at the top? I know a lot of people do couch their opinions in terms of who the leader of the party is but we don't vote directly for them. I don't fully understand where these debates fit into British politics other than to appease some weird yearning to be more like the American system.
And finally, I agree with the leader of the DUP that the broadcasters have overstepped the mark. They're just broadcasters. Yet there is this uncomfortable sense that they're calling the shots in this election. They've already tried to dictate who the major parties are, they have only grudgingly agreed to have a debate with 7 talking heads at all. Cameron has pretty much stuck to his guns for the whole process - he actually said in the quote they keep playing "Let's get moving on this, let's have this debate."
Everyone else looks oddly pathetic. There is all sorts of bravado from the other parties and the representatives of the broadcasters- if they run an empty chair debate without the incumbent PM, they will just look petty. He's not refusing to debate he's just saying do it at a sensible time.
And let's face it, these are not going to be real debates anyway. The whole thing will just devolve into meaningless soundbites and petty point scoring, constant interruptions a la Question Time and each Party leader is just going to ignore the actual questions asked and just force everything back to the main talking points that their debate prep teams have told them about.
TL;DR: It's debatable (bdum tish) how much worth these debates would have had anyway, and I think Cameron was right to stick by his guns. Down vote away.