The appeal of UKIP
Because the real story of the election is UKIP. They clearly won more votes on the day than any other party, and if the campaign had gone on longer may well have won the whole thing. Why? Before answering, it's worth pointing out that I agree with the Dude on UKIP. I think it's an unserious party, and that it is the largest single example of the Fundamental Heffer Error, in that the party wilfully conflates what it wishes were the case with what is actually the case.
That being said, their brand of Poujadist populism is proving pretty effective. Tim Montgomerie trawled through their current policies before the by-election and found that the major points are a promise to cut taxes for "everyone" and abolish Employers' National Insurance. This substantial reduction in revenue is coupled with no cuts to frontline services, bringing back student grants, creating a "million jobs" through public and private investment, hiring more police and building more prisons. They also want to spend an additional 1% of GDP on defence. And, presumably, a pony.
The intention is to make people nod approvingly at each individual policy, without having to join them up. It's a terrific opposition strategy (and it would have been truly ironic if this brand of telling people only what they want to hear had jin fact beaten the Liberal Democrats - last season's brand of telling people only what they want to hear). This does raise a question though - if UKIP isn't really a serious party, are the people voting for it deluded, or stupid, or something else? I dislike writing off an electorate as stupid (Vicky Pryce juries aside). It's arrogant, and almost always wrong. There is, in any event, a better answer here. UKIP has made a position for itself as the anti-politics party. Just at present, there is almost no better position to be in.
Will it last? It may well do - provided the economy doesn't recover. People are disillusioned and angry with all the major parties; UKIP are the channel for 'none of the above'. It'll make 2015 even more interesting.