Adding to those explanations, even though I'm not sure of what you mean exactly, I note that on-the-field upgrades wouldn't make too much sense for anything but systems turrets, and even some of those wouldn't make too much sense.
Homeworld "explains" that auto-upgrade capability with the existance of component-scale production facilities within every ship (and ship production facilities on capital ships), but that requires units with larger scale than in warzone, to make sense (for example, a standard fighter in HW: Cataclysm is about 100 meters long and not too much less wide).
But recycling is necessary to Warzone - its "Strategy by Design" moto requires to carefully choose when to keep researching and which units to produce, as well as if you'll mass-produce or will specialize groups and keep focusing on research. The variety is more than a hundred times bigger than in any Homeworld (or many other RTS games, as well as many TBS as well)
Hope this was insightful but not boring
~Olrox
