Going by the listing available, I will say these are for console only at this time. No idea if Prima plans on a PC version of the guide. Time will tell.
Amazon has listed a Prima Guide for The Sims 3 Pets. No idea for which platform, but it is listed on Amazon without a description for which Platform.
Buy.com has one listed but for the Console version only, Playstation.
Play.com also has a listing. Thanks Ducky!