What was missed was an explanation of the answer, so here it is. Yes, this involves thinking. If your brain is comfortably coasting on idle, feel free to ignore this.

You know how when you're counting and you go from 9 to 10? You see how the number of digits increased from 1 to 2? Well that means that our basic counting system has a base of 10, so when you reach the base, it starts filling another digit. Same happens going from 99 to 100; and 999 to 1,000.

On a sidenote, this is how binary (the computer language) works. It's all zero's and one's because it's base 2. so in binary, it goes from 0 to 1 to 10 to 11 to 100.

Anywho, the point of this is to explain hexadecimal. With hexadecimal, the base is 16. Which means (you guessed it!) the second digit doesn't start until 16. Well how do they fill the difference between 9 and 15?? With letters, of course!

9 decimal = 9 hex

10 dec = A hex

11 dec = B hex

12 dec = C hex

13 dec = D hex

14 dec = E hex

15 dec = F hex

16 dec = 10 hex

Don't worry, I was confused too.

Well, as you can see, the letters D, E and A are all hex numbers. So when the riddle says "How many people know hexadecimal if only you and dead people know hexadecimal?" it implies sneakily that dead is a number, not a word. So:

dead hex = 57,005 dec

you = 1 dec

Therefore, dead + you = 57,006 decimal.

Sadly, my fellow geek Christopher figured this riddle out in about... 3 seconds. Which made even me feel slightly retarded.

Pleasant headache-free days to all.