The "extended partition" stuff works differently. You designate the last partition (let's say number 4) as extended and this allows you to create more partitions inside numbered 5, 6, etc. So after that you realy have block devices /dev/foo5 and /dev/foo6 along with your /dev/foo1 etc.
But what ixtab says gives sense. You have also the partition table on the exported usb drive. But I always thought that this is only virtual.