IOTA was born as the answer to the Bitcoin's weak spot : its transaction relay network.
Bitcoin needs a bigger relay network to maintain the daily growing number of transactions. Today most of the transactions are relayed within seconds, but some of them may take several minutes to be relayed or are relayed by a node (relay) that is not in the neighborhood at all... To have an efficient network, the relays have to be many and have to be evenly distributed around the globe to propagate transactions very fast.
Bitcoin is different from state currencies because coins are issued as a reward. Miners creates and maintain the transaction database (the blockchain) like a ledger, they secure the entire database through a computing effort and get rewards for doing so. Today it represents 25 bitcoins for a block added to the chain (a secured page of the ledger). Miners work is very real : supercomputing units (ASIC), huge energy consumption, evenly cooling needs, and lot of space to host the whole thing like data centers or mining farms. Still, these costs are well covered by the reward in bitcoins.
So what about Bitcoin's backbone ? Its relay network.
The nodes are not rewarded in any kind for their part of the work : relay all the transactions in bitcoins trough the network and list all the transactions for the miners to be secured in the blockchain.
IOTA announce a rewarded Bitcoin relay node.