Clustered double listings (which I think you're describing) are getting rarer as Google experiments with different serps arrangements.
Clustering occurs when you've got two pages returned on the same serps page for the same query. When Google has clustering on (generally what they've been doing for the past many years), if you had a #2 position and moved another of your pages up to #10, the #10 would be clustered together with #2 and be moved up to the #3 position and indented.
If you're really dominant for a query (say one of the words is in your company name), you may get additional listings, possibly a group of 4, or possibly a plus icon to show more results from....
As Google plays with different serps arrangements, not all multiple listings are clustered. I've seen a domain have a #2 and a #9, position, eg (that's pulling an example out of the air, but I'm relatively sure I've seen it).
A risk of targeting the same terms too often is that you're putting many eggs in one basket, and you may end up wasting inbound link equity that might be better used targeting a variety of phrases.
I get the feeling hes only ranking now because he got that double listing and is therefore more trusted.
He's got the double-listing because he is more trusted, at least in a given word-space. There's a chicken and egg aspect to this, though, since several unique pages on the same topic can reenforce each other, if they are respected enough to gather independent relevant inbound links... and different enough that Google feels that both are worth returning.