Of course you could just say that this once again confirms what you already knew--that RDF is irrelevant and of no use to man or beast, but bear with me for a moment.
The fact that you and I 'know' that this mark-up means that 'Mark Birbeck' is located at a certain geographic location is a kind of 'implicit knowledge' that we have overlaid onto the scant information we've been given. But what if the web page we were dealing with didn't concern a person, but a company? Could we assume that it now means that the company is at the specified location? Perhaps. So what if the page also contained product information? How do we know whether the location information is to apply to the company or the product that is on the page?
In other words, having some kind of accepted behaviour for metadata, or relying on some kind of implicit (or 'domain') knowledge, only gets us so far...which is not very far at all.
Don't get me wrong, this information is still pretty useful when presented to humans, since they can usually 'fill in the gaps'. For example, if we had a web browser extension that showed a map with a little red cross on it whenever the page we were viewing contained location information, that would still be pretty handy; when we were looking at someone's home page we'd assume that the map showed us where the person lived (although it might be where they are now), and if we were looking at a museum web site we'd assume that the cross showed where the museum was located (although if it's a museum of items from another country it could be the location of the country).
And if we were looking at the 'ambiguous' example I gave above (of a company page that also contained a product description), we might still be able to make use of the location information given to us by our browser extension, and deduce from reading the web-page text that the map was showing us the company's location, or the product's, or neither.
In short, we can go a long way with this kind of 'flat' information structure, adding pretty much any 'tags' we like and relying on our 'implicit' knowledge to match up the meanings correctly. But we'd just have to be aware that outside of the world of this document, the metadata we have is pretty useless unless a system also knows these implicit meanings.