As far as I know the images can be used without ant issues.
They were recreated icons, not the original icons. They only look similar. (Hard to tell at that size and resolution.)
Just search "icons and you will find tons of recreated free icon packs in the Internet that look similar to the program's icons.
Furthermore, when web sites post documents (the US federal government, US state governments, universities, and businesses) they use (and can use) the actual icons to represent the document type. By default, if you have a free reader/player program (acrobat reader, ms powerpoint reader, abobe flash player, apple quicktime player) on your computer (desktop, server, mobile device) by default it assigns it's native program icon to that file type.
It is the same manner that people use twitter, facebook, digg, etc icons as buttons to link to their feeds.