Domain name relevancy certainly helps and to this point is very important. If the site's content is represents the domain's name then you have an advantage.
Multiple domains same thing. Till the SEs change their algos. However if you now start setting up domain names with entire sentences you may be out of luck. For instance 2-3 keywords is ok. 10 keywords is not.
I assume because one of the page properties SEs look for - at the moment is overall length of the URLs + meaningful keywords. Shorter urls still have advantages.