So my questions, what is so mysterious about dutch light, if that is the most important component to achieve this effect? If not then what is going on behind these images. Are they heavily post-processed, are they multi-exposure stacked images for HDR?
It's important to appreciate that what you're looking at in this flickr set is a gallery prints for sale, probably the work of several years by a professional photographer.
To answer your question as best I can...
As far as I know, light in the Netherlands is of the same nature as light in any other place of comparable latitude! Clearly the photographer has spent a long time scouting locations and waiting for exactly the right atmospheric conditions, but even so there's clearly some sort of filtration going on.
It's hard to say whether it's all Photoshop, or lens mounted filters, or a combination of both. The detail and contrast in the sky points to either multi-exposure HDR, or graduated filters. There's a lot of vignetting in some of the images, which is either done with filters or in Photoshop. The overall soft look and warm colours certainly resembles a blurred layer with the blending mode set to overlay, but that's probably not the only way to get the effect.
Check out the artists flickr profile: http://www.flickr.com/people/42443389@N00/
In it she states: "I enjoy drawing by old-fashioned hand. In the fall of 1995 I bought the programme “Fractal Design Painter” (then still 4.0 Version) and got my first taste of the fantastic digital atelier that such software has on offer."
That seems to imply there is post-processing on these. She left contact info in the profile. Send her an email asking her how she makes those photos. You never know, she might just tell you.
Just thought I would let you know that this whole process is described in detail in the latest (September 2011) Popular Photography (Canada). It in fact has to do a lot with natural light in the Netherlands which is unobstructed by obstacles and mountains. The photographer interviewed in the article is an artist by training and the effect she is trying to reproduce is that of the classic Dutch landscape painters. As far as equipment goes I believe she uses an Olympus DSLR and filters which are often used together. She also explains the photoshop post-processing workflow.
Nothing Dutch about that light (though the scenes are familiar) :)
Looks like heavy use of tobacco, ND, and in cases soft filters, vignetting applied either through multiple filters or in post processing.