What would you suggest then? Using USB portable drives and cables? It is so not convenient. What is intended for primary storage if not NAS?
As, I think, Jeremy said, if you're going to store your images on a network device then a high speed ethernet connection to that device would be the better way to go. USB external drives aren't all that fast either (maybe OK with USB 3). Plus it gets messy when you start having multiple external drives stacked on top of each other. I use a small external drive on the road so that I have 2 copies of all my images - one on the laptop hard drive, one on the external - in case something happens with one I still have the other to transfer to my main computer in the office.
I've got 4 internal 1TB drives for images, a 120GB SSD for the OS/software and a 6th 250GB drive that's got a bit of non-photography related data on it but it's primarily used as a scratch disk. Everything gets backed up regularly and automatically via ethernet to my NAS which has 3x2TB drives in a RAID 5 (4TB total storage). The automated backup doesn't include the LR catalogue because that gets done each week via LR when I shut it down. The catalogue is backed up to the NAS. The automated backup does include a system image. Ideally I'd have a second NAS with one stored away from my office and swap them out but the budget doesn't allow for that at the moment.