I think the only advantage to a TC is it's design profile. If it is located in a very visible area, like a desk or with a TV, etc, it looks nicer than an AEBS with a few HDD's hanging off of it (along with all the USB cables, power bricks and cords). If you don't mind a little more clutter, I think the AEBS w usb-HDD is a very good option. At least, if either the router or HDD dies, you only have to repurchase half the system.
No, because most of NAS units off redundancy (various levels of RAID), and more robust software to configuring and using the product. TC is good if you want to stay on Apple, and don't do much else other then using it to backup.