I wouldn't think that this applies to all devices.
Macs hold their value on the used market pretty well and is not usually set by the base model, especially if there are certain upgrades, such as GPU. Some upgrades do not always hold in value though.
Good luck finding a year old used iMac in good condition @ 50%.
As for cars, I wouldn't say that this applies either, unless you re talking about wholesale markets. Although, I guess this might depend on the model.
I think that the Apple Watch would be similar to iPhones though, maybe not as dramatic of a price loss, but similar.