Oh, we're sorry your computer doesn't come with a PDF viewer, but does everything else you need. Would you hate it if you had to download every codec so you could enjoy your MP3s, oggs, FLACs, m4as, etc? If you had to download xvid and divx for your video files? If you had to download libraries so you could run games?
pdf is the standard for printable documents, and many manuals are downloadable in .pdf format.
They're quite small, and they aren't ugly. In fact, I don't find many eBooks outside of .pdf format.
Macintosh is a small fraction of the total number of desktop computers in the world. If it's a standard in Mac, accept it.
Lossless PDF files are very very good quality. If it's an image, it's practically perfect.