Why are coinbase transaction outputs greater than reward? If the sum of the coinbase transaction's outputs must be less than or equal to the current reward (25 btc currently), why in practice do blocks have a slightly higher coinbase transaction output (for example this block has a coinbase transaction with an output value of 25.25058085 BTC.
The extra 0.25058085 BTC is the sum of the transaction fees on the block (each transactions fee is the difference between the value of the transaction's inputs and the transaction's outputs). 

As you can see, this block which had no transactions on it, and therefore no transaction fees, had a coinbase transaction whose sum of outputs was exactly equal to the reward (50 btc at the time).