The main difference is that these buttons require no images, while the Zurb ones still require an image. The lack of images makes the buttons highly scalable.
On Github there's a version of the Zerb buttons that's pure CSS. I haven't tried it in IE, but it looks good on Safari and Firefox: http://github.com/gr2m/awesome-buttons.
Agreed. That is their main downside but honestly I haven't had any issues with them setup that way. I've been reusing them for both images big and small and it seems to come out alright.