In The Mac mini: Comparing Apples and Oranges, Dan Frakes breaks down the pricing for Apple’s low-cost system and a “comparable” $399 Dell system that journalists all over the planet seem to think is a fair comparison. Unlike all those other journalists, he actually compares everything that comes in the box or pre-installed on the hard drive.
The nutshell is, the Dell is missing a lot. If you need any of those things (and some of them, such as anti-virus software, are essential to everyone running Windows), the Dell stops being so cheap.