I think it is possible that some people are not buying as many new computers as often since with internet services like Netflix, Hulu, YouTube, Onlive, Gaikai, and streaming services, people can watch an almost unlimited amount of videos, shows, movies, and games without filling up their hard drive full of video files and installers for a low monthly cost of 10 dollars or less.
But, for more heavy users like online gamers who use Steam, and people who prefer to pay to download files off of iTunes, Amazon, MP3/video, Steam, and download stores, they will be more likely to buy a computer with a larger hard drive and faster speeds to fit all the videos, games and MP3 files which they bought online to their hard drive.
I think most people just use their current computer till they break if they mainly use their PC for blogging, NetFlix, YouTube, online music + video, and cloud gaming on Onlive, and Gaikai since most computers these days can handle most of the everyday things people do online.
I heard Netbooks are pretty good if you just want to go online, but the screen size is kind of small, so you might want to buy an external monitor.
Jolicloud is a good Netbook operating system which is slim, fast, stable, and does not use a lot of space on your hard drive. You can also get a Google Chrome based Netbook, Macbook Air, and Windows based Netbook for going online.
