Writing occupies a peculiar place in all of the many vocations one can embrace. I can't think of any other field where newcomers are more eager to hear the advice of their elders (sometimes as a way of putting off actually writing.) Nor can I think of any other field where the grand old men so readily dissuade newcomers from making a go at it. I don't believe that's what Rod intended to do with that entry, but professional writers almost always tell the newcomers that: 1) Writing is a tough racket; 2) they themselves were lucky to get in when they did and their career path is probably not a possibility anymore; and 3) the market is changing in a way that's made it more difficult than ever to make a living at it.
Far be it from me to pooh pooh the wisdom of our elders, but come on gentlemen. You're not saying anything we haven't heard before. Of course it's difficult; everything worth doing is. Obviously half of all writers are going to be below average. Sure, you'll pay your dues and suffer a lot. But people who really want to write are not going to let any of that slow them down. I don't make any money from this blog but here I sit clickety clacking away. Writing is like any other skill: the more you do it, the better at it you'll become.
Mainstream publishers might eventually go the way of the dodo, but today it's easier than ever to publish something thanks to the interwebs. The hard part is getting discovered. I'm actually rather surprised at how many views this blog has gotten considering how lazy I am about self-promotion. Writing is hard work, sure. But sometimes you have to do it because there's nothing else you can do. Those sort of people should absolutely persevere to the end.