A newline character on Windows is a carriage return plus a linefeed. Hence the System.Environment.Newline constant. If someone ports the framework to some other platform, a newline character may only be a carriage return or a linefeed on its own. vbCrLf will always be both.
Having said that, anyone who ports the framework will almost undoubtedly be trying to be compatible with the Windows one, so they'll leave it as a carriage return and linefeed.