"From what I've seen" meaning I've seen them out of stock in all stores where I live and online. I'm not posting factual data, nor did I ever make that claim. I'm just saying that observation and common sense contradict the assertion in the article.
I'm highlighting dishonest, misleading journalism. The author claims that the iPads undersold, but there are no hard numbers nor no comparison to how it should have sold. It's just a bunch of hooey. It's easy to find an article asserting the exact opposite, e.g.
http://www.businessinsider.com/ipad-mini-sales-2012-12
Just because some of you personally don't like Apple doesn't magically make the Ipad Mini a dud. I personally don't like the poor choices for screen and hardware, but most people don't seem to care.
And while I'm at it the OP's quote is out of context, the article is not about the Ipad Mini, it's about whether Apple will innovate enough to convince people to buy an overpriced tv with the apple logo. Their speculation on the Mini is only meant as a supporting statement to bolster the argument.
These kind of fluff articles are largely meaningless and are quickly forgotten once we know more about the tech (in this case the apple tv). This has happened again and again. Don't take it as gospel that the Mini isn't doing well.