Dog clippers (good ones anyway), have a higher running speed to them (some have 2 speeds), which helps the blades clip the thicker finer hair of the dog. You might get through a dog's coat with a human clipper, but you could potentially wreck his coat, as the blades may just kind of 'crunch' through the hair, rather than cut it cleanly, like the faster stronger pet clipper will. If you spend the money on a decent clipper, it should outlast your dog...I have clippers from over 10 years ago, and they are still used daily (I groom dogs and cats)...so they have definitely 'earned' their asking price!!!!
As far as checking out horse clippers, unless you have a large breed dog I highly discourage this, as they are really bulky, and there is no way you will reach all the areas, and definitely no way you will get into small spaces, like armpits, and groin areas, without possibly cutting the dog's skin. You also will not be able to change blades on these livestock clippers easily. Yes, they are powerful, but that's overkill for a dog!
Ummm...most of Andis' clippers have the permanent rotar...I have all Andis clippers and they have stood up to everything! I have two speeds (of various versions), as well as a cordless...They have all 'paid for themselves'.
All of my corded clippers were around the 120-130 range new, and my cordless with extra battery, and corded adaptor costed me around 280 new. ALL are over two years old...with my oldest one being around 10-11 (still usable)...