Stock is only useful if honored by the company management. If you have to trust them (which you do) they might as well just maintain the share register (which is exactly how it currently works, although most companies outsource the maintenance of the database).
There's no point in using a complicated proof-of-work system to maintain a simple spreadsheet when at the end of the day you're effectively just going to print off a copy and hand it to someone and just trust that they do whatever it says. They might as well maintain it centrally as it's much simpler. There's no value add for this huge p2p network crunching thousands of Ghash/s when at the end of the day someone can just ignore it.
And? At the end of the day, a human can ignore my bitcoins. At the end of the day, a company can ignore my Charles Schwab stock purchase. All they are are ones and zeroes in a computer, just like those dollars my bank claims I possess.
A distributed, notarized database of digital tokens has a large number of uses that may extend directly into real world goods. It is readily apparent that value exists in a neutral, distributed entity maintaining a database rather than a single entity (== single point of failure).
The only reason the bitcoin network works for bitcoins is there are no external trust dependencies. That won't be true in the case of any of the physical goods trading you described.
Not true at all. Bitcoins would have zero value, if you could not trade them for real-world goods, services and currencies. People trust that the value of their bitcoins will be there tomorrow. That is the mother of all external trust dependencies.
And you miss the point yet again. I think I've explained what I meant fairly well already so I'll probably just give up now.
A human could ignore your bitcoins.. for example they could buy some from you and then not do anythin with them. I think you'll agree that isn't really your problem. If you buy something from them using bitcoins and they ignore your request for goods and keep the bitcoins then they're a dishonest trader, and you lose out - but that doesn't affect the rest of the market. There are other honest traders out there that you can deal with.
The difference is, in that situation it's just a bad trader, in the other situation the entire market has to be cleared by a central authority - the corn dealer or company management. If they turn out to be a bad trader the entire market is invalid and it doesn't matter what system you used to record who owns what, because nobody owns anything because the guy that's supposed to ultimately give it to everyone has ripped you all off. Similarly if the guy is honest, it doesn't matter how he records who he owes what too. It could be a block chain, but it could just be a free spreadsheet in google apps.
There probably are some other uses of proof-of-work distributed block databases, just not the ones that you've presented so far.