Lets take the Spellthief's line for example.
With the old items, you'd spend 850 total gold to buy a Frostfang.
This item granted anywhere between up to 144 gold per minute.
With the new items, you spend 400 gold to buy a Spellthief's Edge.
In its base form, this item grants up to 102 gold per minute.
As Frostfang, it grants up to 108 gold per minute.
As Shard of True Ice, it grants up to 18 gold per minute.
This means that once you've earned 1000 gold with the item (which could be done in 6.94 minutes if the old Frostfang was used opimally), the item gives virtually no gold.
But hey, a free item is saving you some gold, so that's worth a good bit, right?
In the first place, no support player worth their salt bothered upgrading their old support items past tier 2.
This means that you're only saving the 450 gold it cost to upgrade the damn item, which is more than made up for by how much gold you miss out on.
Sure, when you hit your T3 support item you get a spike. Who gives a shit? Sure, the support has a 60 AP item.
You think they wouldn't rather have the money to buy items?
It's funny, in a way.
Remember in Seasons 1 and 2, when people avoided playing Support because they had no way to get gold?
When your only items were Boots, Wards, GP10, and maybe 1-2 utility items if you were lucky?
Well, now you spend 400 gold on a GP10 item at the start of the game.
Over the item's lifetime, it generates around enough gold for Upgraded boots.
Meanwhile, your innate gold generation and kill participation might allow you to purchase an Ardent Censer.
We've come full circle. The only difference is that now, the other guys with items can burst you down even faster and easier, and you can't even buy wards to stop that from happening.