Weight can be a crucial factor, but is more pertinent for the lower cost entry-level AVRs (SRP <$999). The power transformer is the most expensive component within an AVR, and the primary mass-distributed brands including Yamaha, Pioneer, Sony, Onkyo, Denon save $ by
reducing here. The other key build factor is to consider the heat sinking area, when there is less heat sinking area and then the AVR has to bring in the protection circuit sooner. And the output stage will have less thermal capacity. However as previously mentioned, once the SRP is > $999 then there are simply more $ available to use higher grade components.
The other consideration is that the entry-level AVR user is more likely to use a subwoofer/satellite loudspeaker system. Whereas the low frequencies are handled by the subwoofer's amplifier outside the AVR which relaxes the demands on the AVR's power supply and built-in amplifiers..
Just my $0.01..