I remember this... i believe they created it this way so that they can add the heatsink on the other side of the pcb... but i wonder if it would hurt the asic when another heatsink would be directly on the chip. I mean cant this lead only to even more heat dissipation?

About install extra heat-sinks on each avalon chip: please do not do that. there is a air gap between the die and package top, install a heatsink on chip is useless. and will cause overheating. because the top PCB copper act as a heatsink too. do not cover them.