Here is my problem with this in a nutshell.
If a person picks up a dollar bill in the street, it is not theft.
If a person picks up a $100 bill in the street, it is not theft.
If a person finds my wedding band that I lost in the ocean it is not theft. (true story)
In all these cases the person's abandonment of the object relinquishes ownership of the item. Wedding band might be a little more legally confusing in the presence of a law like California's, but moving forward.
The theft only comes into question in legal terms when the original owner somehow protests the possession of an item by a second party. The process of people acquiring possession of abandoned items occurs every day, and in this case the phone was abandoned. To come back after the fact and say I want item X back is all well in good but you should never expect to get X back.
If you can prove you own it and that the item is indeed yours, you are entitled to have it returned to you regardless of the items current possessor. A person who finds an item should not be legally obligated to find the person the item belongs nor make any effort to find that person. (There are huge differences between legal and moral obligations.) I lost my wallet once, it had my drivers license in it that had my address, it is clear who it belonged to so the person that found my wallet is guilty of theft? perhaps in the eyes of the law but not in my eyes! The real legal issue should have been between gizmodo and this guy for selling gizmodo something that he did not have the right to sell. (and gizmodo knew what they were getting, a prototype iphone does not just show up in media hands, they had to at least consider it was a hot item.) Apple really isn't owned anything in my eyes after they were fortunate to get their device back.
I am not a lawyer and I know there are major differences between misplaced, abandonded and so on in the legal world. So don't overanalyze the vernacular in this comment. In my eyes if you forget it you abandoned it (isn't that what they call if you leave behind your child for 2 seconds. a child is never misplaced.)