Well, we are also forgetting the fact that may be the marrying couple are interested in postcard size prints and the photographer doing it for free is going to just give them the files probably even without processing them.
Some people usually confuse the fact that someone who buys a DSLR and has a couple of expensive lenses are great photographers, or more precisely great portrait and wedding shooters.
I recently was looking at a wedding album of a close friend including the DVD with the images and she had spent a huge amount of money for the wedding shoot and tried to be very diplomatic and did not point at so many obvious errors such as harsh shadows etc amongst some of the obvious problems with the images including very bad lighting, some images that could have done with a bit of processing to balance the light, backgrounds etc. Did not want to lie also and say they were good. Just managed to get around saying anything directly to do with the quality of the shoot.
As it happened I was there (Africa) to do some work around rural areas and she was going to accompany me on a 1800 mile trip across the country and as she had a keen interest in photography during the trip I let her use my kit for several occasions and was teaching her the basics and giving her tips etc. Surprise surprise after returning from the trip she started moaning about how bad her wedding images were and pointing the very aspects I had been teaching her like how to avoid harsh shadows etc.
Conclusion of this is many times a viewer realises how bad photos are when they can compare them with some that have been nicely taken or when they become aware of mistakes that are not supposed to be there.
I even asked her why was she saying her wedding pics were not well taken and she immediately went like: Oh look at those shadows around my head, and look they are so fuzzy, they look out of focus etc etc.