"Apple has popularized tablet computers with its iPads."
But in actuality, Apple popularized the iPad only. Most other tablets did not sell well enough to be noticed. Such as the HP touchpad. And the Motorola Zoom.
"That is hurting PC sales in the U.S. and other industrialized countries."
Actually, PC sales have been growing double digits and are still growing. The only problem lately has been supply of hard drives. Emerging countries, which has a huge population, are choosing the PC or laptops in general over any gadgets that just surf the web and are limited by applications. The real product that has been hurting because of iPads and iPhone popularity is Apple's own iPods which dropped in sales significantly over prior years.
"Smartphones such as Apple's iPhones are also delaying PC replacements among consumers."
Not true. Laptop sales were accelerating ever since the iPhone came out. Maybe some consumers may delay PC replacement, but the majority will go ahead with PC replacements since the newer versions do more while costing less. The deals are so tempting that I put a desktop in two seperate rooms to enjoy the 24 inch screens which no mobile products provide. Just like people have $500 to $1000 flat screen TV's in more than one room, people will choose to have desktops in multiple rooms as well for their kids or guests. So it does not make sense to say that iPhones are in actuallity delaying PC replacement. Currently, the demand for PC's is higher than supply due to Hard drive issues which are expected to fully be resolved in the next 3 months or so.
The original iPad was set to go after Netbook sales. To even think that an iPad can replace a PC is funny. It's something you buy in addition to a PC. If your house burns down and you can only have a PC or a tablet what do you honestly think most people would choose?