Any commodity tech is the same. I'd bet a Mac would hold its value way better than a similarly spec'd generic PC.
Absolutely. The last few Macs I've sold have sold for about 70-80% of the price I bought them for new.
My last Macbook Pro I paid about £900 for and sold for £650. The Macbook I had before that was £899, I sold that for £700.
My last desktop PC cost around £800, 3 years later I swapped it for a crate of beer, the one before that I gave away. There is no money in selling used-PCs, but Macs certainly keep their value.