I saw his/her post and wondered how long it would take for someone to reply with an implication that he/she was not fair to women PCs. It's a tired old argument that has been going on since 1e. I think there are many reasons why one can ignore "realism" when dealing with strength values, some of which you just mentioned. I myself don't use strength limitation anymore because it's really not that big of a deal. That said, I can easily see how someone would like to cap STR for halflings or gnomes without them also being unfair to any particular gender. An adult male and female are a lot more similar in size than an adult and a 6 year old. Not sure why you are thinking that by applying that limit to halflings and gnomes, they have to apply "realism" to everything. Maybe that's just how they like to run their campaign world. Nothing wrong with that, and they certainly don't need to make extra justifications beyond what they already gave.
I.e., "men vs. women? Meh, close enough in size so no reason to have a different. Adult vs. a 40lb 3 ft tall person? That's much bigger of a difference. Barbarians ending up with super strength? Class feature, not a natural born trait."