i dunno. to me your cousins look like each other, and like you, and basically like most other mammal on earth. two legs, two hands, one head. you're a crazy nitpicking nerd if you pay attention to differences between your cousins and monkeys, they are basically the same design.
Nice comparison pics.
Honestly, the people who don't care about the differences...each to their own. But they are usually not real fans of the license and they just want 'an alien' toy in their collection. same deal with the other people who just want an 'endo' or an 'iron man'. I don't give a rat's behind about Star Wars and all Darth Vaders look same to me..but I know for the real fans his appearance in each movie is slightly different.
All these differences say between Robocop 1 & 2, different aliens and predators, different endo...are negligible to the non-fan or even casual fans, which is fine. But yeah it's pretty blind of them to just dismiss the differences.
When you get serious about collecting..that's what these minute details comes down to. Just a common example take a Rolex submariner..look the freaking same to the average joe, but to the collector every model year has subtle differences in the font, case width, etc that people pay tens of thousands for. It's fine if you don't appreciate it..but doesn't mean it's not there.