1st. Why do they look so similar to Nazghul's (i mean the mount not the rider)?

http://elderscrolls.wikia.com/wiki/The_Elder_Scrolls_V:_Dragonborn?file=Dragonborn-trailer-12.PNG

http://images2.wikia.nocookie.net/__cb20110913194327/lotr/images/4/4c/Nazgul_Fell-Beast_3.jpg

I mean i really like the idea that so much looks similar to LotR in Skyrim but isn't that abit too far? xD

2nd Where are they????

I only encountered two in my whole game. One of them was story related >.<

It's a level thing. They are tough so you have to level up a bit first. I've killed a ton of them now.
Also it's probably a LotR easter egg