Additional character requirements do increase security.
When you write a program to try every possible combination, special characters, numbers and capitalization requirements all increase the combination set you have to run through.
The problem is it's fucking pointless because a 10 letter password is unbreakable. A super computer may be able to break a hundred digit password in a matter of minutes, but if the super computer is 10ms across the internet, it might as well be a 486. It would be over 30 years just to try every combination in a numeric password, you'll be dead a thousand years before a 10 letter password gets hacked over the internet, barring revolutionary leaps in networking that remove latency from the equation.
Sites like this seem to think you're going to be using the login server to crack the passwords.
Now if you used a dictionary word, well... There's only a couple hundred thousand after all, even over the internet a password that weak can be broken. Then again, any system worth a damn should be doing a lockout after 3 failed attempts in a row. If something is trying to log in four hours straight, they have bigger security problems than password strength.
Where it will matter is when they get hacked.