Interesting question. Probably there are several factors that lead to this better performance than most British operators have.
1. The Netherlands are a smaller country, with trains running shorter distances. The Dutch don't have long distance trains covering 500 miles in 5 hours. The longest domestic service covers not even half that distance. On international services to for instance Berlin, Brussels and Frankfurt large delays are more common because on larger distances the chances of delay are greater. Most domestic services are in travel distance as well as frequencies comparable with c2c or Chiltern Railways. And indeed those operators are among the better performing train operators.
2. The Dutch railways cancel trains sooner if they are running too late. On most lines trains are running in a 15 or 30 minute interval, so if a train is running say 25 minutes late, it can easily be cancelled because the next train will be there in 5 minutes. Cancelled trains won't be counted in the punctuality performances.
3. Because Dutch and other continental railways don't have to deal with the restricting UK loading gauge, they can run twelve car double deckers with possible train lengths of 340 metres. Around London however, train operators are still struggling to lengthen their trains to 200 or 240 metres single deck length. Therefore they need to run more trains to provide at least the capacity the Dutch have, leading to a more congested railway network, or full trains with irritated passengers, or both.
4. As a Dutch I have the impression we have sorted out our infrastructure better than the Brits. Frequencies of more than 8 trains per hour on a two-track line are a reason for doublin to four tracks. The desired timetable leads to the infrastructure that fits best, in stead of the other way round. There where the desired timetables of two trains conflict with each other, the section of track is declared congested and a study is started to find the most effective alteration to the infrastructure. In the Randstad (large urban area in the West of the Netherlands) there are almost no conflicting movements between trains because of grade separated junctions; a large contrast with railway lines in South-London or in the Northern urban areas.
These are the reasons I can think of to start with, but there are pobably lots of other factors.