Firstly, Ed didn't apologise for Iraq. He said Blair was wrong and Britain was mistaken to follow America's lead in ignoring international opposition to the invasion. So no, if Jeremy gets the opportunity he will be the only leader to have said sorry for Iraq. As for the 2005 general election, you might say Blair wasn't punished electorally but in the long-term, the party certainly was. Thanks to their initial opposition to the Iraq War before the first bomb dropped, the LibDems surged to 22% of the vote. Six million votes only gave them 62 seats, but those voters stayed put five years later. Other Labour voters dropped out, or drifted to other parties. The only reason why the Tories didn't do better was because Michael Howard's leadership had a touch of nudge, nudge, wink, wink racism about it, and he was a complete has been. Once again, it wasn't Tony's unique talents that won us the general election - it was the disarray and incompetence of his opponents.
More toxic was the effect Iraq had on the party and mainstream politics more generally. Each constituency party suffered dozens of resignations, including hard-to-replace key activists. With the Tories and Labour agreeing that attacking Iraq was necessary, cynicism toward the centre left and centre right of politics was entrenched. This isn't to say anti-politics wasn't a thing before the first cruise missiles slammed into Baghdad, but it was redoubled by the arrogance with which the largest demonstration in modern political history was dismissed. And that's before we even start talking about the dodgy dossier and the tissue of fabricated "facts" cooked up by the State Department and British Intelligence. Whether Blair and other ministers lied to get the outcome they wished is a moot point: it was widely perceived that they had.
Does this matter now? Absolutely. From within the Labour Party, Jeremy is the repository not just of left populism but also anti-establishment politics sentiment. By declaring this now, Jez is making a very clear statement about the kind of party Labour needs to be - one that is engaged with and animated by its members and supporters, not one that treats its support as a "core" to be neglected because it has nowhere else to go. An honest apology can, for some, go a bit of the distance needed to re-win popular trust in politics generally, and our party in particular.
Whether it's a dead cat tactic or not, it's a position his opponents would find it hard to respond to. Before today, it was Yvette Cooper who had made Iraq a campaign issue and was among the first of Labour's big beasts to break cover all the way back in 2007. Andy Burnham has stayed schtum, but back in 2010 he stood by the Iraq decision and thought it was time to move on. And Liz Kendall, who knows? Whether their responses are "it doesn't matter" or "intervention was right", it paints them into a corner normally reserved for unwashed wallflowers and they look even more out of touch - if that was possible. Also, Jeremy (and at a push, Yvette) pre-empts any damaging political fall out from the forever-delayed Chilcott inquiry. No doubt the Tories will be looking to use it to damage Labour, despite their voting along with the war - including messrs Dave and Osborne.
Necessary? Yes. Timely? Yes. Politically smart? Absolutely.