The home computer market increased rapidly due to the Internet. So you can assume that most people have computers for the Internet.
So tablets and phones do replace the computer for most people.
Those doing computer art, music, 3D graphics, websites and coding obviously still need a traditional machine to do it well.
I don't disagree but my comments were aimed squarely at the average user, who'll have mostly modest requirements besides maybe playing games.
Right now it's still a little impractical (if for no reason other than cost) but in many ways tablets make just as good desktop replacements as laptops, use an external mouse, keyboard and monitor and the lines become very blurred between what's a desktop and what's a tablet.
I have a decent desktop machine for my work (web design/development with .net) so I have no reason to buy anything else currently but I see no reason a Surface Pro wouldn't make a perfectly suitable device to work from once hooked up to the same accessories.
I do think there is a limit as to how big phones can get before they become pointless as a mobile device. Perhaps if they perfect those rollable displays we can at least roll up the screen.
No one (?) wants a bigger device than is necessary of course but I don't see why people are annoyed at the size of devices like the Note 2 or 920 as the majority of the market is using a 4 inch or smaller screen and I like having choices.
The pursuit of an ever smaller device doesn't always make them better, I found an iPhone 4 to be more comfortable with a bumper despite the size increase and Apple could have crushed the competition if they hadn't shrunk the depth and used that extra space for the battery (there are other areas such as monitors/TVs where the pursuit for an ever smaller bezel has given us worse image quality but let's not get sidetracked you hopefully get my point).
I'll concede that a lot of the 'flagship' models are big phones but that's fairly logical as it takes time to adapt the latest technology to smaller sizes, the 920 is big because it has a large battery, wireless charging and optical image stabilisation, if you want a small phone you have to sacrifice some or all of those features.