Can you get me out from this confusion

Anil
Ravi,Pinak,Suki you people have worried lot when i asked my doubt(fact)
Why is it called building when it is already built???
!!
Below are some doubts(obviously facts) of similar feather...
* If people from Poland are called Poles, why aren't people from Holland called Holes?
*If you're not supposed to drink and drive, then why do bars have parking lots?
* Why the man who invests all your money called a broker?