Clearances (the distance between parts) haven't changed much in almost 100 years for production engines. Tolerances (the allowed level of deviation from spec) have indeed improved due to better manufacturing practices, but that doesn't change the oil grade requirement.
An anecdote:
Back when the Ford Windsor 302 "HO" engines were being assembled, they were hand-built. The engines were bored to a nominal size and the appropriate size piston was determined, then ground down to a specific weight by removing material from around the wist pin area (this is part of balancing) and then the rods received the same treatment, and were stamped with the cylinder number they were intended for. Because of the hand-assembled nature of these engines, the tolerances were quite tight.
When the LSx truck engines were being produced, GM went with bulk fit piston/bore configurations. That is, there were "binned" parts that were slapped together, the block was bulk machine bored and honed and they used shorter piston skirts to reduce friction. This process (the piston to bore fitment) had some rather loose tolerances and, combined with the short skirted pistons, meant that some engines had some pretty loose piston/bore assemblies. When cold, these pistons would "slap" the bores, which is why the early LSx truck/SUV engines became somewhat notorious for being piston slappers. It had no real impact on longevity, but it was an annoying byproduct of that bulk-fit process. Later on, they put a teflon coating on the skirts to reduce (or eliminate) the noise. I don't know if they tightened up the manufacturing tolerances or not or if the same level of deviation was still allowed with the updated pistons.