I have been playing with this today, and it is true. I have the latest version of Opera on Windows and have successfully used border-radius without a vendor prefix. It uses the specific corner versions that webkit does rather than the way mozilla does (these do the same thing, first if mozilla, second in opera):

-moz-border-radius-topleft: 200px 300px;
-moz-border-radius-topright: 200px 300px;
-moz-border-radius-bottomleft: 200px;
-moz-border-radius-bottomright: 200px;
border-top-left-radius: 200px 300px;
border-top-right-radius: 200px 300px;
border-bottom-left-radius: 200px;
border-bottom-right-radius: 200px;