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Both sites have DMOZ listings and a few other good links - PR is similar (higher on the site that has vanished if anything)
Both have .co.uk domain names
The biggest difference is the server they are hosted on. One is hosted on a UK based reseller account and the other a US based one. The one on the US hosting is fine, the one on the UK hosting is gone.
Besides IP address there is a small amount of cross-linking between some of the sites on the UK server - as a local webmaster I imagine this is pretty common.
Anyway that's my most controlled observation on this update.