I find engineering one of those 'primary professions' that could be replicated on most characters someone has, unless you only care for gold making you can replicate those gold-making professions on most characters. Engineering doesn't have much gold-making items, but its utility, transportation increase, gadgets (Plumerang,FAC-TEUR) are too useful to not use it as one of the primary professions, at least on some classes. But nevertheless, if you're doing what's on this article, you should have 5+ characters to make it to the profit, but even then, putting, let's say, alchemy+herbalism on ALL those characters would be a waste of time and resources. I myself have ALL professions, Alchemy on 2 characters (both Goblins, for obvious reasons), and only 2-3 of almost 20 leveled characters don't have engineering, and can tackle 99% of the world's profession needs.But people have the choice to do it as they please haha.
I wish I had realized it was Super Squirt day. Last time Wowhead mentioned it was coming up so I kept looking at the new articles to see if it was mentioned. I didn't realize that it's mention would be put in the economy page.