Heavy partial deads have definitely put on size and strength, to a noticeable extent, along with squats that i do the day before my back workout. This translates over to chest, where im stronger and much of it is due to deads and squats.
I think your body has a switch and it makes you maintain some form of balance and symetry-in other words squats/deads turn the switch on and allows your entire body to grow-and if you neglect them, you will be stuck at whatever level you are.