Well, I can't say I know how to turn all who copy/paste into people whom actually post, trying to give a more conscious welcome, not only for post count or whatever.True
Now,that you have pointed out the problem how about looking for a solution.
Something we can do about this.
They will do as they please, we can only do as much to change that, so I think that the best thing to do is to give our own welcomes in a fashion that makes the new ones feel welcomed, by being interactive.
Also, I've started to urge them on to tell us more than a simple 'sup..' by asking them to say more. As OhReary explained, it is hard when you don't have much to reply to/work with, so ask them to introduce themselves properly instead

Do you have any ideas?