Usually they'd factor in how games advanced since, possibly knock it some for "just" being a full HD update, or maybe there's some other reason they'd give a slightly lower score such as super high scores are meant for hot new releases rather than just warmed up releases unless said release was completely remade.
And while I defended the objective angle to a degree up there, it can also be subjective as to how much those components matter. Ueda games frequently have performance issues, but should those really hold a game down that is so amazing and unprecedented otherwise? Or even further, could a janky control scheme like RE5's work in the game's favor? What about something like Deadly Premonition that is flat in the game department but offers enough to allow you to get through that with relative ease to see the completely kooky experience beyond that? Hell, maybe the "bad gameplay" is still fun anyway, kind of like a stupid cheap, unhealthy snack.
A thought of mine is that objectivity probably matters most when you KNOW a part of a game didn't sit well with you and it wasn't compensated for in some way to truly overlook it. Like a poor UI you struggle through that really had no business being so poor, or something. Which just feeds back into why reviews are subjective in the first place, as that's why games can get marked down period.
