You could give them the benefit of the doubt and assume it's just the fact that they're saved as gif images for no obvious reason that's making them look less clean. But that fact alone (and the URLs for the images) just underlines Microsoft not getting the web at an institutional scale.

(I don't think a 256 colour gif would actually be that bad since it's mostly monochrome, but they appear to have dithered the greys while at the same time having a rainbow of unused colours in the palette.)

edit: actually only the red one is a gif, but only the rightmost one is both a png and links to a larger image (like the .gif does) rather than the exact same image. I think the text looks better (the phone case certainly does) but it might just be because it's white on black instead of vice-versa.