All the measures mentioned in the rules are actually standard measures in "Thickness" in any Swedish timber-yard shop. So the lenght of the various pieces are the measures "made up" somewhere deep down in history. Pine is also the most common type of wood in the very same Swedish timber-yard shop. Go to IKEA and you'll see a lot of Pine. The Pine poles that are cut for Kubbs and Kings are used in building various details when building houses, like a porch or a fence. A good Gotland Kubb set is made of the Pine core, witch is very hard and something else than the rest of the tree.
As for the rounded edges, in Rone they have early (not BRIO, I'll come back to that) sets that have the corner edges phased off. Those are very difficult to throw in when the surface is dry like in 2013, or as it was in 2008. Those very old kubbs are mixed in with newer pieces. These newer ones mostly, I say mostly, have edges that are rounded, but still edges, if that make any sense? As opposite to a sharp edge. I would say that the game Andreas refers to in his post (I'm BTW proud to be Grandpa to AI Gel, the hedgehog ;) ) have those rounded edges. In short, I would say there are three levels of corners, the phased, the rounded sharp and the sharp. Hope this claryfies a little bit.
As for BRIO, they made games for sale that where (at least) two pieces of wood glued together. They were to some extent used in Rone, but have sort of outranged themselves by splitting themselves up into smaller pieces. They are very rare by now, if any. The BRIO games didn't always measure a full 7 cm on the kubbs as well, they where to my knowledge just 6,5x6,5x15 cm. Me and my friends still have some BRIO games, one set have a King that looks like a mummy. Others have kubbs that are screwed together and we always turns them to get the screws pointing backwards, to save the batons... We use them winter time.