Well, they had to make those versions different from the Saturn version, otherwise they wouldn't sell as well, so they made two unplayable characters playable and made them so powerful that anybody could just pick them and use them to their fullest without any problems.
And as a side note, Trilogy is considered part of the canon, as the story there does supersede MK3's, and references Shinnok with Mileena and Noob Saibot.

Adding Noob and Rain was an easy way to add characters. They had to cut so much else from the game including Sheeva. They probably wanted to still have something to add to the game.

It didn't have many levels, it was missing tons of sound effects, it had frames cut out everywhere. UMK3 was the same size as MK3. Everything they added for UMK3 came at the price of removing something from MK3.

Because Midway decided to be nice and get rid of Sheeva for some good characters.

Are you serious dreemernj?It was the same size as mk3?See for some reason i dont understand that,cause the genesis verison has more levels and their names are said when you select them other then the snes verison which is I guess is a smaller game in itself.
In a way i can see what your saying if your comparing the snes verison of mk3 to the snes verison of umk3.But I dunno....just seems odd.

ALso to the person who said it wouldnt sell if they didnt had rain and noob to make it different..well when i bought it and this is when i was 13 or 14 i think,i had no idea noob and rain were in it,actually I just wanted the arcade game and was alittle depressed about it. Updated for dreemernj, I was just looking up and interesting enough, Snes verison of mk3 is 3.35megs where as snes umk3 is 3.29mb.But remember how i said umk3 for the genesis has more stuff in it compared to the snes verison of it?Well ok,cause umk3 on the genesis is 3.19mb and mk3 on there is 3.22mb.Now I am no video game expert but if umk3 on sega can hold more with less memory then the snes verison should hold more cause it is a larger file.Hopefully your get what I am tring to say.

UMK3 Genesis, UMK3 SNES, MK3 Genesis, MK3 SNES are all the same size. 4MB.

For sales and to get people to also buy MKT, IMO they could have left Rain and Noob Saibot out and kept Sheeva in because they didn't have any finishing moves, just brutality on the Genesis version, babality, stage fatality, and brutality in the Snes version, also Shao Kahn doesn't annonce names in the Genesis version either.

4 mb might have been the total size of the cart itself but 4mb was not used for the games in any of the verisons.

What do you base this on? If you dump a cart you get just about 4096B of data. It's not like the ROM chips are packed with zeros or ones or something.