iostat shows large amount of activity

Quick question. I have an LVM volume group set up with 2 logigal volumes. One of the volumes only contains the binary logs. When I watch the speed at which the logs grow with ls -al command, they are growing about 1MB every 3-4 seconds, yet iostat shows my write MB/s around 4-5. Anyone know why this could be?

Anyone have any idea what would cause the difference in these numbers? Is it normal?