I often see that transition dated to 2006 at MacWorld, but the reality is that it was previewed at WWDC the previous year and there was only a minor spec bump to - I think - one model before the iMacs appeared to kick things off.
On a related note, I was not surprised - but definitely disappointed - to hear them describe the iMac changes as "making the computer disappear." Such 'appliances' have always seemed cheap and purposefully limited (not in a good way), yet this is what the market seems to want.
Regular people continue to not understand how computers work and they probably never will.