boot question

I have an external 4 port usb2 hub with my printer and external HD attached. The first time I boot up the system it never gets attached. ( I can do a lsusb command and the hub does not show) If I then do a sudo reboot it comes back up with the usb hub and HD working. Why does this happen? What changes on boot up the 2nd time? I also would like to fix this but right now I'm simply wondering how this happens. Does udev have something to do with this? Thanks Roger