This may have been because a) Clegg's performance in the first debate led to a lot of polls where LD support was high, but ultimately this support melted away by the election and the history bias kept polls wrong until the last minute, or b) because there were lots of Polly Toynbees telling pollsters "I'm voting lib dem" to make sure they were in with a chance in the coverage, but actually intending to vote Labour (she actually advocated this tactic of lying to pollsters in the Guardian.)
Either way, it shows that statistical averages of what people say they'll do isn't always a good indicator of what they'll actually do when push comes to shove.
Disclaimer: as a (now rather embarrassed) Lib Dem, I'd quite like these predictions to be more accurate so I don't get my hopes up again.
I have no idea about the political culture in the UK. Is it possible that he just didn't have as much data to work with? In other words, a lot fewer relevant polls to feed into a model?
we don't generally have very many regional polls, and certainly not constituency polls, that are available for aggregators (an internal poll in a key marginal, perhaps.) There's a lot less money spent on UK elections.
In reading his analysis of the election here, he repeatedly mentions that having only two candidates makes things much more predictable.
In any case, we don't know if he got it "wrong" unless we know what % chance he gave this outcome. (He tries to account for the likelihood that polls are misleadingly biased, and that would correlate across multiple seats.)
Silver predicted: Conservative 312, Labour 204, Libdem 103 Actual result : Conservative 307, Labour 258, Libdem 57