Frederick Giasson has written a tutorial article on using the semantic web to integrate data and make new use of data found on the web using semantic web technologies and approaches.
He shows the steps needed to create working applications, from data transformation to user interface. At the end, there is a working example that is available online.
This means that data only matters. In fact, the only thing one need now is to build a good data source. Once the data source is well built (remember, the data source can be anything here, from a search engine database to the products catalogue of a company, or even the personal web page of a 14 years old geek).
From that data source, everything can be generated for each web page (URL). If the content requested is a HTML page, then the data source can generate XML, run a XSLT skin template with and then send a HTML page: just like any other web page. However, from the same data source, a semantic web crawler could request the RDF/N3 data for the same URL. Then the DDWP would send the RDF/N3 representation of the URL.
So from one data source, you can get its data the way you want.
From that point a URL (or a web page, call it the way you want) become a presentation page web, a web service, etc; All-in-one!