The article misses a more likely reason for the declining sales: maybe sales of the iPad are declining - not because the iPad has lost its appeal - but because the market is saturating and most people who wanted an iPad, have already got one. Folks who have iPads that are 3 or 4 year old are not in the market for newer models - as the old ones are working just fine.
I think there's a lot to this. My house has one iPad (an iPad 2) that still works great and gets daily use by everyone in the family. We have about four or five Macs, three of which are working but my laptop is the only one that gets much use. We also have 6 or 7 iPhones, two on a current plan, one the kid uses to play games, one is used as an alarm clock in the bedroom, the rest are gathering dust in a drawer. So even though it's probably our most used device it's less than 10% of our Apple hardware stock.