Yeah, Sudoku has nothing to do with numbers. Replace with the letters A-I or colours or breeds of dog, and it'd work just as well.
The Killer sudoku OTOH does rely on maths as well as logic, and they're seriously hard!
I've got an electronic one (a tie-in one from the Times) which Emma gave me, Xmas before last. I almost always solve them, even on top setting - I'm rarely stumped or get the logic wrong. The battle then is for times. I rarely bother with the "easy" and "mild" levels, because the time is more down to how fast you can navigate round the game screen than sudoku skill.
Re your question, PoppaGator, apparently that was the big problem. It took him minutes to figure out the game, and then years to figure out the maths behind putting a rating on how hard they are (and whether they can be completed at all)!