The Point: "Modern Browsers" are the browsers that actually get around to actually @#$@ing SHIPPING new features and NOT TAKING FOREVER TO DO IT. Iterate faster and get new crap to users NOW.
thing is, 'new crap' is also unfamiliar crap. Unfamiliar to developers. 5 browsers, 5 teams of developers, results is 5 different ways of doing things. -moz-border-radius and the like are BAD for the web, because everyone shipped new crap without any kind of agreement on how it was supposed to work. And now we've got vendor specific code in our websites. That's not how the web is supposed to work.
Impatient browser vendors shipping unfinished specs like css3 are as bad as proprietary spec extensions like 'filter' etc.