This post brings up an interesting question that has been running around in the back of my mind for some time. My recent trip has allowed me to add some context to my thoughts.
The OP is correct there is a Bias for sure. But I am not sure it is connected to the Class A's. I think it's larger than that. To me the Bias is towards parks that are more the "Resort" type. Full of, in many cases, useless "amenities" that most never use.
There are many very good parks with all gravel spaces that because of their setting (scenic) or their Location (perhaps on the beach.) Should rate as highly or higher than some of the big 300 space parks with concrete, pools, shuffleboard, pot lucks and all the rest. But these smaller simpler parks often get shunned based on the Good Sam criteria for what makes a good RV Park.
There needs to be a Handicapping system to even out the ratings so that smaller, friendlier, more scenic or better located parks can get higher ratings. Or revise the rating system to accomodate a range of other types of "positives" rather than the huge resort type parks.
There is also a real bias in the guide for Good Sam Parks. I feel that the non GSP's are in some cases not getting fair reviews.