The idea that a site ranks better if the keyword matches the domain name exacty is a myth. The fact is that it will rank better is usually because a naked link going to your site has the keyword(s) in it (w w .keyword1-keyword2.com) and Google simply parses the URL as text (anchor text). I got this straight from Leslie Rhodie of Stompernet and SEOBraintrust fame. Just get your title tags and content density correct and that will go a long way as as far as on-page optimization goes
LOL - I am on the edge of showing you my own websites with exact match, wordpress installed, and only a couple of links outranking wikipedia, about.com, amazon etc.
But, since I don't want to reveal my niches, all I can say is that your statement is simply not true. I did a split test - 2 same type websites (wordpress) with similar content (~80% original, but with same keyword density, titles, meta tags etc).
One website had exact match domain, other had relevant domain as well but it was not exact match domain. The first (exact match) was ranking no.7 WITHOUT A SINGLE LINK after about a week, while the other website (relevant domain, but not exact match) was NOWHERE TO BE FOUND.
CONCLUSION: No1, and I repeat no1, knows for sure not just this small detail with exact match domain but all other SEO tricks and details. Only guys working in Google itself (probably) know it, but I am willing to bet that only select few people know the whole algorithm since it is so damn valuable that I guess Google company doesn't want to risk revealing top secret data to their employees who might get offers from competing companies looking to find out that damn G algorithm.
No matter what someone tells you, be it Lesley Rhode or Matt damn Cuts, trust only yourself and what you see from your own tests.
Peace out
rovad