He also left a comment here, part of which I will make bold to reproduce:
As to RDF underpinning the Linked Data Web - it is only as necessary as HTML was to the growth of the Web itself. Documents were being posted on the Internet in all sorts of formats well before Tim Berners-Lee introduced us to the open and shared HTML format which facilitated the exponential growth of the Web. Some of the above comments are very reminiscent of the "why do I need to use HTML" discussions from the mid 1990's.
It is an open and shared format, such as RDF, that will power the exponential growth of the Linked Data web, but the conversations around it are still at the equivalent of 1995 stage.
What Richard is saying (again, as I read it) is more subtle: widespread growth of the data web requires an open standard to cut through the Babel of competing and closed formats the same way that HTML cut through the Babel of document formats, because without that interoperability is too much effort and so no one realizes the benefits.
Richard is welcome to check my understanding; I may have this completely wrong. Nonetheless, I don't believe a word of it, and I especially don't believe it if RDF is the HTML analogue (which, let's be clear, Richard very carefully did not say). Here's why I don't.
First, HTML was hardly the only part of the web stack necessary to its explosion. TCP/IP, anyone? Moreover, HTML by itself is obviously insufficient as the driver of that explosion, or we'd all still be on Gopher (remember Gopher?). Formatted strings of words are not all we monkeys interact with. Neither are assertions, about documents or anything else. (The whole thing about "not all data are assertions" seems to escape some of the die-hardiest RDF devotees. I keep telling them to express Hamlet in RDF and then we can talk.)
Second, I don't know that we need to rely on a single data format for interoperability. It's not impossible, but remains to be proven. The data web that I personally think is more likely closely resembles today's mashup and microformats cultures: lots of formats with suitable documentation (one hopes) and APIs, available for use by whoever's willing to suss out how the various datasets work and write code to glue them together. It's a rough-and-ready sort of interoperability, arguably an inefficient one, but eppur si muove, as Galileo did not say of the web.
Third, I'm not entirely convinced we need to rely on interoperability and its network effects as our incentive toward data-sharing. Tim BL certainly did; there wasn't much technical precedent for what he was up to. But we have the web already, a cogent argument if ever there was one. We also have governments, grant agencies, and businesses wanting to multiply return on investment in data. RDF seems downright small-potatoes by comparison, as incentives go.
Finally, the HTML:RDF analogy falls down in one area that I think is utterly crucial: ease of adoption. I can teach enough HTML (and CSS) to be going on with in a couple of hours; I've done it. I still touch RDF only with great fear and loathing and a constant sensation that I must be doing it wrong, and I'll teach it only when I absolutely must and with a great many "I don't pretend to understand this" disclaimers. You can't frighten me with XML namespaces, XPath, XSLT, or regexes, but RDF scares me stiff. This is not an open standard that's going to rule the world. Not today, not tomorrow, and in my opinion not ever.
There's another danger lurking in the one-format-to-rule-them-all argument, a danger I hinted at above: what happens to data that for whatever reason aren't expressible in the format of choice? Second-class citizens? Invisible? I hope not.
Anyway, I say again: if the data web depends on RDF, the data web is a pipe dream and we should look for something else to do. I'd much rather believe the "if" clause counterfactual.