There is a difference, but there isn't enough of a difference to a reasonably healthy adult. Most children are comfortable supporting their bodies on gymnasium playground where their butt isn't the seat contact. I wouldn't file that core strength and balance under athlete level.
I don't think this is the point though. The point that there have been plenty of examples of shoulder sitting, that seemingly violate the rules. I think they need to get rid of the rule all together if this is going to be the case. It makes it seem like they're just going to pick and choose who to penalize and that's going to make any team that is penalized feel unfairly targeted. I personally think it's a pointless rule anyway.