Rapid depreciation isn't necessarily a bad thing for business. iPhones rapidly depreciate, and iPhones are pretty much the biggest business on earth.
I've never heard this before-- and in fact most people seem to say the opposite.
Just looked on eBay and according to recent sold listings, as of the past few days a 5 could easily bring $100-150 depending on configuration. That's a 4+ year old phone.
Let's do a comparison that makes sense. The Samsung Galaxy S3 (released at roughly the same time)is currently selling on eBay for $20-50.
Well, duh. I wasn't comparing the iPhone to an actual investment. The Galaxy S3 (released at roughly same time) is now selling for ~$50 on eBay (sometimes a bit higher).