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Just a guess on my part but I'd guess it has something to do with mfg or machining the rims. Some piece of equipment probably uses that to lock part of the rim down while some other assembly or machining process happens. With 2 of them facing each other, it wouldn't be too hard to have 2 claws lock into them.
Just a guess.
By the way, how did you determine that is the cause of your leak? Had a persistent leak on a 79 Olds I bought new. Several times it went in and one tire still leaked. Finally replaced the rim and the problem was gone. The mechanic was persistent, he put a junk tire on it and sank it in water. Every once in a while a bubble came off (actually out of) the rim. Turned out the rim was porous and that was the cause of the leak.
I marked the rim and tire where the bubbles were. pretty constant stream of bubbles.
Not doubting you there, but could it be the bead on the tire that has the problem and not the rim? From the looks, I'd think the tire bead should cover that fairly well. I'm guessing you're not the only person with those indentations in the rim and can't say I've heard of others complaining. Here's a thought, rotate the tire on the rim say 90 degrees and see if the bubbles stay in the same place or not. If they don't move, maybe fill them with something like J-B Weld, sand it down then mount your tire.