I don't think thats enierly fair, I'm no lover of Labour but i think David had the sense to realise that it would have been more difficult for his brother to get elected if he had stayed in the shadow cabinet. I mean, the media was already becoming obssessive over the whole 'cain and able' metaphors, it would have been 10 times worse if David had stayed, leaving Labour a bigger farce than it already is.
Its been proven time and again that the politics of the actual left are unopopular with the country, and you don't get elected. Thats what happened to Labour in 1983, it takes something like the second world war to deliver a genuine socialist party with a decent mandate (as in 1945).
Labour are out dated and obsessed with statism still, they can't see that the country has moved on. I notice Ed Miliband was still even talking about '5 year plans' for industry like any former soviet premier. Hopefully the AV referendum passes and at the next election we can secure real proportional representation. then we can have all sorts of views represented. I'm a traditional Liberal (market and social) but I wouldn't mind working in coalition with any party/s that delivered a half decent platform on the things I care about.