Lets compare the 600 dollar Mac Mini to a 600 dollar HP. I'll even give Apple the credit and only source from HPs website not Newegg or another source you can get it cheaper or taking advantage of sales on HPs site. I'm giving Apple every advantage here basically
The Mac Mini has a 2.5 GHz i5 dual core processor, 4 GB 1600 MHz DDR3 RAM, 500 Gig SATA Hard Drive 5400 RPM.
The HP Pavillion 500-210qe comes with a 3.0 GHz i5 quad core processor (4430, apple doesn't specify which one they have), 6GB of Ram, 1 TB 7200 RPM Sata, DVD Burner (not an option with the Mac Mini) and comes with mouse and keyboard (Mac Mini does not)
So to compare, the PC for the same price has a much faster processor, twice the hard drive that's faster, and 2 more gigs of RAM.
Compare All-in-Ones? iMacs start at 1300 bucks, HP I'm comparing it to is 1250.
iMac has a 2.7 GHz i5 quadcore processor, 8 GB ram, 1 TB 5400 RPM Sata, Intel Iris Graphics Apple Magic Mouse, and Keyboard with a 21.5 inch 1920x1080 resolution screen.
The HP Envy Recline has a 2.9GHz i5 quadcore processor, 8GB ram, 1 TB hybrid HD, nVidia GEForce GT730A, HP Wireless Keyboard and mouse 23 inch 1920x1080 resolution screen
To compare for 50 bucks less you get a bigger (though lower resolution screen) slightly faster processor, way faster hard drive (hybrids are estimated to be 4x faster than 7200) and better graphics card.
Of course the difference again, I can go to a site like newegg, and get cheaper better computers which isn't an option with Apple.
The one area they're close is high end laptops. And that's about it.