Cheers, i was thinking it was something a little more technical than that....lol
It is. In every transaction, there is a field called the scriptsig for the input. Since a coinbase transaction doesn't have an input, anything can be put in the scriptsig. Most miners will then put something in the scriptsig that identifies which miner mined that block. However, this is not guaranteed to be accurate since any miner can put any message there. It can be spoofed.
The IP address of the miner/pool node that relays the block that is solved is also available and can be compared to know mining pool addresses. If you notice when it's an unknown miner who solved the block the IP is listed instead of the pool name.
No. It is not possible to know the IP address from which a block or transaction originated. Blockchain.info only lists the IP address of the first node which relayed the block or transaction to it. That node is not necessarily the node that created the block or tx.