Stretching the screen would cause distortion issues, 4:3 image on a 16:9 widescreen HDTV would make the fighters look like oompa loompas. If they didn't have side bars to keep the original proportions, people would complain the screen was too stretched out.
We're talking about games made between 1992-1995. They'd look as good filling up your 55 inch TV as a standard definition episode of the Wonder Years would.
Also how many times did Midway make money off the original games? I only recall the Midway Arcade Treasures and adding them as bonus material for deluxe editions of the main series games. Other than MK2 on PSN and UMK on XBL, I don't recall them directly selling the original trilogy on current gen consoles.
Besides, I don't think a gun will spring out from either console demanding that this be purchased. If it's not your bag, so be it. Personally, it's a day one purchase for me even if playing MK1 online will be a mind-f for me.