Frequency
The sealed for life policy of the smaller more efficient units may incur greater frequency of replacements. This may outweigh their smaller per unit eco impact against one longer lived large old unit.
However I do not believe eco is the force 4 change as much as the bottom line.
Many Business users have not changed their XP pc's because they are considered still fit for purpose, so will stick more RAM in it, replace Hdd's to increase return on investment.
Sealed for life takes that option away placing the risk of premuture replacement costs through failure or under specing on them. So the onus should be upon the manufacturers to prove to the users that the inherent reliability from these production methods are capable yielding the required return on capital.
