Really, this rule shouldn't be in place for explorations. When exploring for people, it should be okay to specify where the comp planets are.
I believe this rule came in about (i think anyway, i wasn't here at the time), was to stop this kind of thing:
"I'll give you a NAP, but you pay me 5 planets. These 5 planets are to be x, y, z, a and b, because they give me shares with Fam XXXX."
^ That kinda thing used to happen yearssssss ago in Milky Way - and imo, at the time everyone agreed it was bad practice/form. Yet people would still do it, without it being an official rule.