Hedera has a fee associated with all transactions (that are submitted to the network) and most queries (that are sent to a single node) Fees fund node payments, prevent spam and DDoS and so help secure the network.
When the user looks up their balance, they are charged a small fee to compensate the node that returns the balance.
Currently, all fees are constant for every action; once the mainnet transitions from early access to open access fees will better reflect the differing impact of the various transactions and queries.
In the future, individual nodes will have the ability to define their own fees for queries and some may choose to make the account query free. Additionally, mirror nodes will allow such queries to be off-loaded from the main network, and so could well be offered for free.