Can someone explain to me why the Enclave, back in 2240 or so, decided to put a big glowing amber circle on the back of their "Advanced" Power Armor?
I understand why we have LED fans in our modern gaming PCs (they look cool), but people don't usually shoot at those.

because it looks http://tvtropes.org/pmwiki/pmwiki.php/Main/RuleOfCool.

The previous model had a transparent trouser window, it is at least an improvement on that.