I'm not entirely sure how the reward system in Bitcoin works.
So, every 10 minutes a block is solved and 25 bitcoins are rewarded to a miner (or group). This happens in proportion to the amount of total computation power that miner has invested in solving the block. So a miner that has 30% of the total network power has a 30% chance of getting the 25 bitcoins and so gets roughly 8 bitcoins every 10 minutes right? If it was a group of 4 miners, average payout would be 2 bitcoins per minder I think.
How do transaction fees work with this? So a block consists of transactions. Are all fees for all transactions summed up and added to the basic 25 bitcoin reward and hence rewarded according to the same probability as above?
In addition, does this mean that a certain block can be worth much more than another one, should somebody be particularly generous in his transaction fee?