You need to know the history of EMDs (exact match domains) in Google's results so you can fully understand what's going on.
Before Sept 2012, Google gave a "boost" in the rankings to domains that were EMDs. So if you had Keyword.com you were given a boost if in rankings if someone searched for "keyword".
In Sept 2012, Google rolled out the "EMD Update" algorithm update, which got rid of the boost. So, rather than getting a boost for using keyword.com for 'keyword', there was no boost available. Every domain supposedly is now created equal.
But, Google has a lot of ranking factors, one of which is related to 'anchor text' of links pointing to your site.
If you have Keyword.com, then there is a VERY good chance that other sites linking to you will think of you and mention you as being "Keyword", thus you actually get an indirect ranking boost. The anchor text of links pointing to you include "keyword" or "keyword.com", which helps your rankings.
That is why it's still important to buy and use a keyword rich domain name. It helps your rankings in Google 'indirectly', not because of the fact that Google is giving you a boost for having the keyword in your domain name.
By the way, it's important to note that Bing appears to give you a boost in rankings for "keyword" if you're using something like keyword(.com) as your domain name.