For the average person to buy something you need to buy a coin, that's 1 transaction on the block chain. They need to buy something with that coin that's transaction #2. The merchant needs to sell that coin that's transaction #3. Granted #1 and #3 can be much larger reducing the costs, but the average user is likely to be splitting #1 across a small number of transactions.

Further 2 exchange fees sit on of those 3 coin transactions.

In theory you can have an exchange handle all 5 of these transactions, but then your using the exchanges book's not a block chain.