Just found this pretty informative article on reddit: http://www.4p8.com/eric.brasseur/gamma.html
Tried scaling down a few of the example images in Paint.NET by 50% and it seems that we also make the same sorts of mistakes as Photoshop and many other image editing software out there. Just a heads up to the devs, Paint.NET could do with changing the scaling algorithms for 'best quality' etc