why don't haste items stack?

i have a cloak that provides 10 haste
and also have the flowing black silk sash from an old hq that provides 15 haste
but it seems i can only benefit from one or the other's haste, cause if i equip both my Haste mod is 15
so should i assume that haste on items never stacks?
and if so, can anyone suggest a logical reason for this?
and does a haste spell stack with a haste item? assuming it does
finally, r there other benefits that don't stack?

Shock
70 Bruiser
Bazaar

what i was told by an uber bruiser is that you can only have one haste item and one haste spell

There is one exception... the 2% adornment hastes stack with anything, including themselves.

There's an adornment that gives 20% haste to twohanded weapons, but that one counts as item haste.

You can have many haste spells active and they do stack, Monk for exampe have 3 haste buffs themselves that all stack and they also stack with Truby and Illusionist spells as well as shammie pet aa haste. I thought haste adornment were supposed to stack but as far as im aware that is broken, apart from that only the highest haste item will work with any other haste items being ignored.

What's the name of the 20% haste aug for 2h weapons, and do you know the req'd level?

What Haste augs can I find for a 42 Bruiser?

Thanks

get the + 10 dps mods for neck and wrist items

Don't forget the Judicious Easyloader and Rousing Cry Master I if you really want to max +dps mods.