Software support for this programming model is certainly more immature. To prove this concept and model, we need the presence of a large amount of data on the Web. We also need a number of shared vocabularies with which to leverage our connections between applications. Developing vocabularies is hard, and promoting them even harder. While I applaud the work done by the Dublin Core committee, the average level of education of XML programmers on Dublin Core is pretty poor.
Vocabularies remain a very difficult problem.
It's obvious that at the moment we're not at the HTML point. XML-based language that could achieve this vision of distributed data, has been around for a good while now and yet has still not caught on. There are examples, however, of this working. By far the most common use of this has been as a lightweight syndication format for links to news stories on sites. Meerkat would be useless if it weren't for the feedback loop that caused web site owners to create XML-based metadata about their documents.