The mysterious number 6174

I was roaming around the web, when I saw this particular web page, explaining the mystery of the number 6174. Read it to the end, and you will feel happy that you learnt something new.
So what's the mystery of the number 6174? Well, it's sort of like a mathematical puzzle. You need to do the following steps:
1. Take any 4 digit number where all 4 digits are not the same (so you can't select 9999), so for example, take 3456
2. Rearrange the digits to get the largest and smallest number: so you get 3456 and 6543
3. Subtract them, so you get 6543-3456 = 3087
4. Do this again with the resultant number, so you get 8730 - 378 = 8352
5. Again repeat 4, so you get 6174
6. Do it again, 7641-1467 = 6174
The number repeated itself, and will do so again and again, no matter which 4 digit number you take.
For 3 digits number, you get 495