Edit: As of August 2016, it is no longer required to have a Google Plus Profile to leave a comment in Google Play Store.
However, it would still require great sacrifices to comment anonymously in Google Play Store as you have to remove your Google+ Profile and as long as you create one again, all your "previously anonymous" comments will immediately be linked back to your new G+ profile.
Note: The following text is obsolete. Refer to above.Previously,
Due to Google's requirement since November 2012, a Google+ profile is required to leave comments under contents from Google Play Store, as is discussed here. All those comments from anonymous users without a Google+ Profile are left before Nov, 2012.