I set up a Truffle sample project, which contains the following contract:

        import "ConvertLib.sol";

        contract MetaCoin {
          mapping (address => uint) balances;

            event Transfer(address indexed _from, address indexed _to, uint256 _value);

            function MetaCoin() {
                balances[tx.origin] = 10000;
            }

            function sendCoin(address receiver, uint amount) returns(bool sufficient) {
                if (balances[msg.sender] < amount) return false;
                balances[msg.sender] -= amount;
                balances[receiver] += amount;
                Transfer(msg.sender, receiver, amount);
                return true;
            }
            function getBalanceInEth(address addr) returns(uint){
                return ConvertLib.convert(getBalance(addr),2);
            }
            function getBalance(address addr) returns(uint) {
                return balances[addr];
            }
        }

The two last functions only return a value and don't alter the state of the network. Why was there no `constant` used for these two functions? From what I can tell looking at the logs, in their current form, both functions need mining and cost gas when being called.