Treasure By Level
1) Characters created at higher levels receive half as much gold.
2) The amount of uncommon magic items the PC has. At 6th level the PC can trade 2 uncommon items in for 1 rare item and at 13th level the PC can trade 2 rare items in for 1 very rare item.
Gold was based on average rolls for all treasure found on level appropriate tables in the DMG. Magic items used similar tables but divided the d100 roll into equal parts based on the level range with lower levels getting the lower rewards. The probability of getting a magic item of a certain rarity was calculated for each level and numbers were assigned based on the results. Numbers were also thrown around to ensure that you get something at every level.
Personally I think the gold gets out of hand at higher levels as there is nothing to spend it on, so I'm not adverse to lowering it significantly. You don't need that many consumables.