Optimal ram speed is obtained by having the ram ICs soldered directly on the mainboard, as close to the (also soldered) cpu as possible, at the cost of easy upgradability - an easy choice for those who only think of the next quarter.

So, I mean the ram ICs can have the solder joints attaching them to datacenter boards melted, and the ICs can be resoldered to the standard ram sticks consumers use in their PCs and laptops. This can be done with home equipment, but not efficiently.