Re: I may be misunderstanding the process but...
"down to Wikipedia's search optimisation rather than Google"
I think there are three possibilities:
1 WP is just a demonstrably good source of information on a large number of topics and therefore wins in a fair fight against other sites.
2 The actual algorithms that Google (and other search engines) use give preference to WP because the human authors thought it would improve search results.
3 WP uses sneaky techniques to game all the search engines.
Given that the SEO "rules" are in constant flux as Google try to outwit their opponents and given that WP have next to no control over 99% of their site's content, I think (3) is unlikely. (2) is unfair, in the sense that only WP can benefit from a hard-coded rule for their domain, but fair in the sense that Google presumably only wrote the rule because WP is consistently better than the SEO-driven crud that they fight on a daily basis. (1) is clearly fair and IMHO might actually be true as long as you steer clear of politicised topics.