Hi Lovinthehd,
First, I wish to thank you for your liking of my thread on the best material for building speaker enclosures.
I entirely agree with you about the option of choosing a beefier power supply which would provide you with full rated power on all channels simultaneously.
However, as you know, in the case of music which normally has a variable amplitude, it would rather be unusual for the amplified source signal content to simultaneously require full output from all channels. The situation would only arise if someone decided to play continuous sine wave signals. The manufacturers know it, and this why, to be competitive they reduce production costs by putting less powerful power supplies.
With regard to the reduction in the weight of audio equipment over the years, the kind of materials used on more recent products such as the finishing with plastic instead of metal, use of more IC's and other more compact components have contributed to it. For instance, with the use of Class D amps, as they are quite a bit more efficient than the Class A and AB types, they generate less heat and don't need heavy heat sinks and/or fans.
The situation does not necessarily mean that the newer products are of less quality or are less reliable. On the contrary, since they use more compact components, that most likely means more air circulation between components, less heat and hopefully better reliability and longer life.
It's good to share positive comments and passion on this site.
Cheers!