Well, don't overstate that too much. I agree that generally the suggestion of PCs main items being in the range of level +1 to level +4 is best, but items are also generally speaking not all that game breaking.
I'd also say that items well below the PCs power level are far from "trash". In fact it may be a bit much the other way around. Especially when you start getting up into high paragon tier and above there are tons of much lower level items or versions of items which can be of very great value to the PCs and had at trivial prices. This is where the daily use limits and slot restrictions really help. Even so you can still run into PCs with backpacks full of implements and such.
Healing potions are a particularly oddball item. They have to be both good enough to be worth paying for and yet bad enough not to be worth using at levels where they are trivially cheap. The fixed HP gain solution actually seems to work pretty well for that. At lower heroic a healing potion is not bad and the cost is enough that PCs won't generally be able to carry vast numbers unless they want to skimp a lot on other stuff. Once you get up towards paragon tier they are dirt cheap, but 10 HP is not worth the cost of a surge. It ends up working out OK. Low level PCs will usually have a few of them around for emergencies and high level PCs will too. Neither group being too overly eager to drink one down, just for different reasons.