True that option is always open to you, but you'll find the resale value of such a beast a few years down the line is very low. Of course you may not wish to resell it, you might continuously upgrade, but this sort of care and nursing isn't open to most people who dont have the skills to do it.
I was on an Android forum the other day, trying to find out how to do something thats stock on iOS for a relatives phone, and the answer was that you can download apps to make it happen. And sure enough enough you can, but it needed 4 apps and then specifically configuring all of them and wpuld probably break with the next OS update.
I could do it but i doubt the average user could (and my relative certainly cant), same with this, you could after all build a Hackintosh but how many people can do that or want to deal with the hassles ?
We are mostly "edge cases" here, i think this comparison is very valid for the Joe Soap user