Yes, true, this, I admit, is strange. Perhaps you are right. I'm not sure how the printing works, though, do the blocks necessarily mean a single transaction? Probably. In that case, I don't think it's simple retail.
What is the percentage of big block/small block buying/selling? If there are way more small blocks going through, then I'd say the big blocks are just retailers with deep pockets.
Hell, Willywizard claims to hold almost a billion shares!!
I do agree, though, that the big blocks are strange. Who's laying that out? But, I wouldn't necessarily dismiss a rich retailer.