A couple things: Firstly, this isn't really "Terminal's" welcome message, because it's got nothing to do with Terminal in particular. It's the "message of the day" file, which is (usually) displayed at login. This can include when you log in from a remote host.

This brings us to the second point: There is a belief, justified or not, that wording like "Welcome to XYZ" may make it harder to prosecute people who break into your system. They may be able to argue, "But it said I was welcome!" Yeah, yeah, I know, it sounds dumb. And I have no idea whether such a thing ever has been successfully argued. But why give potential ammunition to a cracker? Also, some people think you shouldn't give away any information, like even "this is a Darwin system" (not that any cracker with two brain cells to rub together couldn't figure that out in two seconds anyway). Better for /etc/motd to say "UNAUTHORIZED ACCESS PROHIBITED"...

Oh, and vi is not that hard if all you want to do is very basic editing. That said, I still would have recommended nano or similar, given that most readers are not going to be Unix users familiar with vi. Hey, be glad he didn't suggest you use ed.

And that is exactly the reason I made my wife remove that "Welcome" mat at our front door, I didn't want a burglar testifying in court that they thought they were welcome to my stuff...

I've done the same thing as you, removing Welcome from motd files, but it really is silly when you think about it. If that was true, people wouldn't have welcome mats at their front door and instead they would say "keep out" and be covered in red speckle.