I think certain characteristics of certain tobaccos create more or less favorable reviews depending on size.
Sure, some of it may be craftmanship...there's a system by which new rollers "rise in the ranks" so to speak. Relatively inexperienced rollers are only assigned certain sizes to roll, usually babies. As they develop more experience, they gradually move up to more popular sizes, with only seasoned rollers being given belicosos, pyramids and more diffulcult sizes & shapes.
Back to my original statement, with each tobacco having its better and more mediocre aspects, I believe these lend to being a more enjoyable smoke depending on size. I admit, I really don't have alot of variety to my cigar career thus far, but I have had the opportunity to taste different sizes of the same brand and I always have a clear-cut favorite. For example, my love affair with the CAO L'Anniversaire maduro began with the petite, moved to the belicoso, and has since settled on the toro. Each size plays to different strengths & weaknesses of that blend.