For example, if their is a ton of content on platform A which is not on platform B for a specific game, should platform A arguably receive a slightly higher score.

This usually doesn't happen, only notable time was portal 2 recieving a .1 score higher on ps3 than 360 for it's steam integration/cross platform play.

I feel if the exclusive content is significant enough (ala exclusive batman joker missions on ps3) then reviewers should consider, CONSIDER, a higher score even by a fraction, but I reckon their's some sort of stigma.

also batman AO is missing the multiplayer component on wii u, yet it recieves the same score at most reviewers to ps3/360 version when (at launch) it is priced the same.

Yes, depending on the game, It's fair.

If the content is significant sure

If it is significant, yes. Things like the Destiny content on PS don't justify a higher score IMO. But big features like cross-play with PC while the competing console doesn't have that maybe a big +, but also a - since it could break the game.

Technically yes, though exclusive content hardly elevates the game enough to increase the score. Maybe it would increase it in the second or third digit but nothing to affect anything significantly.

Batman with out multi player justifies a lower score obviously