This is where my mind jumped to as well. Especially with regards to the images being comprised of vector graphics, which has always been a pain in the ass to get standard among difference office suites.

Also, if you look between the two versions, you'll see that the Guardian's failed to render the transparency behind the PRISM logo. This definitely points towards rendering mishaps, rather than some sort of editing on their part.

http://www.washingtonpost.com/wp-srv/special/politics/prism-...

http://static.guim.co.uk/sys-images/Guardian/Pix/pictures/20...