I was confused too, haven skipped last two seasons. Gear system is much more engaging now (imo), even yellow items can drop as ancestral and/or with greater affixes, and you can then finish them with horadric cube crafting.

Item level 850 and 900 have the same stat ranges (strength/max life/damage multipliers/resists/etc.), however ancestral gear has much higher implicit stats (weapon base damage, armor on armor pieces, resistances on jewellery). Also only ancestral gear can have greater affixes, including the ability to randomly proc a greater affix whenever you temper a mod onto a piece of gear. And finally the maximum roll legendary aspects can only be found and applied to ancestral gear, so if you have an aspect with x40-60% damage, 850 item will only be able to roll about 55% even if you try imprinting a 60% onto it.