The thing is... I can usually tell a professional photographer as opposed to an amateur.  It is only after looking at a collection though, since an amateur can get lucky.  But, IMO, the problem here is many great photos are great because there is a subject that the photo is trying to portray.  Or there is a certain essence they are trying to capture.  Only problem is if wee have a POTW, people wouldn't understand why a certain photo is so great, since it captured every single thing about that subject, whereas another photo might be of just a random scenery that is pretty.