I think Bernhard was also a rather tall man. You certainly have to put that is in his generational context. The average height has increased quite a bit in the last few generations, so a man born in the mid twenties like Claus would have been among the taller of his peers (mind of course not a giant)
For ex the very tall Dutchmen stood about 5'7" tall at around WWII (Americans were taller by some inches) today while the American have stood their ground and not grown taller (just fatter) the Dutch people have grown to an average of 6'1".
So you see that Claus height is compared to his generation on the taller side as is his sons height, both however are(were) not towering above their contemporaries.
Beatrix however is very small for her generation and it is interesting that her sons are of average or even above average height, considering that
a) the height of the children is said to be linked to the mother, rather than the fathers size
b) most often the first born of same sex children is not the tallest but indeed the shortest.
Which actually makes me wonder if weighing in these facts, Trix and Claus didn't order some Vitaboost to be put into little WAs morning cocoa.....