They're not for the majority of users. You say there is nothing faster than you Mac. So? Who needs something that fast?
For the majority of home users, a Mac isn't cost effective. Why should anyone pay more than £500 for a pc that does everything most of us need, when the cheapest iMac is £800?
You will likely not have to change a MAC as often as you would a PC. Yes, the upfront cost can be more, but not over time it isn't.
If you will never have to replace a PC, only then will I consider your view that Mac's are not cost effective.
Standard application built for PC are also available on Mac. All the standard WP, spreadsheet, DB's, Graphics packages etc are made for Mac's, just as they are for PC Windows.
I use Adobe and MacroMedia products. Now one, and available on both platforms.
MS products are available on Macs,
In other words, applications that the MAJORITY of people use are available on Macs.
I have no wish to argue with which is better, as I have tried to point out; Horses for Courses.