I am using ImageMagick to convert image files and at least the sample above is converted perfectly fine. Since I only have the OSX preview as reference for the psd files I however don´t know if they are all correct.
But seriously, just try ImageMagick as it will make your life a lot easier supporting nearly every format. Sure its a command line tool, but that makes it even more powerful as you can easily integrate it into your workflow.

http://www.imagemagick.org/

The fact that many of the images look the same probably means that they are wrongly converted: http://cld.slindev.com/Uprn
Also its png, because I got that already as "select files -> rightclick -> convert to png" option