It's an important question, because the image that users have of an extension comes mainly from websites. The more an extension is used for websites, the more often people using the net will come across it. And that in turn creates a preference for the extension in question.
1.65 million unique websites active
According to stats compiled by Dataprovider B.V., the Netherlands has a total of 1.65 million unique active websites. That figure includes all extensions, but not redirects, parking pages, placeholders or sites that are under construction. Only sites with multiple pages and their own content were counted. So it seems that only a minority of the nine million Dutch-owned domain names are used for websites. But the actual percentage varies considerably from one extension to another, as the following graph shows.
Percentage of domain names with active websites
Another striking feature of the data presented above is that 'older' domains, such as .nl, .com and .org are used for websites more often than relatively new domains (.eu, .mobi, and the latest generation of nTLDs). Domain names with the newer extensions are frequently registered after their 'legacy' equivalents and many simply point to an existing website with another extension.
Focus on the use of domain names
Dataprovider's figures are food for thought for the domain name industry, which has traditionally been very focused on registration volumes. A domain name without a website may provide income, but it doesn't contribute to an extension's image. And it's far from certain that registrants will have much appetite for retaining domain names in the long term if they aren't in active use. It may well be significant that domains such as .biz, .eu and .mobi contracted in 2016, while .nl and .com continued to grow. There is much to be said, it seems, for focusing on the actual use of domain names, rather than simply on their registration.