It's a feature not a bug
'I am feeling lucky' is not really a lucky dip - it just goes to the top ranked site for that search.
The spammer has got to find a rare word combination, normally some gibberish and then make a site with those words on it. Google will know this is spam, as the numbers of people searching for the gibberish spike, are using I am feeling lucky, and there are very few results for the search.
'The Register' example was a bit off, as www.theregister.co.uk tends to get searches for 'the register' as number one, though feasibly someone could aim for the big domains it would take a lot of effort to usurp them.
I am fairly sure they are working on it now, it is not really a clever scam, as it brings the Google trademark into disrepute and Google are the ones who can identify which domains they are, through quite a few channels actually, when you bear in mind they have gmail.
Google is multi national, so can probably sue for abuse of service and abuse of their trademark wherever the spammers maybe, I think a lot of spammers are going to get a rude awakening with this ill thought out approach.