Sorry, but the Dutch dropped the ball on this one, at least relative to other EU governments. As other folks have pointed out, simple proximity makes the much higher US contribution sensible and sane. But really, the Netherlands, Italy and (especially) Germany need to be up near the UK and France.
In the end, it's their choice based on their values, means, and priorities. The extent to which Americans turn out for private charity is one thing I'm particularly proud of about the USA, but in the end it's everyone's choice individually.
Isn't it entirely possible that the actual aid physically deliverable in the short term has been maximized?
That is, that the Dutch might be better off waiting and raising/sending targeted expertise and funds during the inevitable, but not starting any time soon, reconstruction phase? (Where much of their expertise is something that very few other nations could even offer)
I suppose it wouldn't hurt to pledge that they'll do that now, but any amounts tied to unspecified quantities of work would be fiction anyway. So the number would only be moved for the sake of making it move.
Please tell us more about this reconstruction expertise that few countries have. (The Dutch have unique expertise in reclaiming land from the sea, but that's not relevant to Haiti.)
And, it's not clear that erosion is high on Haiti's list of significant problems.