In a couple of years, with so many coins lost this way, not sure many will be left, since bitcoins are limited to 21 million and losing coins by sending them to wrong address's will keep on happening. Anyone can make a simple mistake copying the address, even though it's easy.
All people who involve in bitcoin know that your bitcoin will loss. You can not recover it.
About the total of bitcoin getting less because of wrong send to any address, it can really happen if no body own the address anymore. If the address where we send it still belong to someone, it means it is just hand over to the other hand.