I'm sad to tell you, but 3e was released 25 years ago, and 4e 17. People who started with those games are oldtimers.
Sure, no-one's stopping players from reading the DMG. But players shouldn't expect to be able to hold guidelines from the DMG over the DM's head. And those guidelines are based on physical limitations, not some metaphysical chakras like in 3e (I don't think chakras was used in the 3e core books, but I've seen devs refer to item slots with that term, and it eventually migrated to Magic of Incarnum which was heavily based around the concept. Can you have two amulets? Sure, why not. Wear all the bling, man. The meaningful limitation is intended to be attunement anyway, not body slots.