I think, and obviously could be wrong, as to why no one seemed to care about leaving their old gen systems behind when Playstation 3 and Xbox 360 came out is that not every single game that was coming out were for next gen and old gen, despite that we have it now.
(Like I said, I could be wrong, so if I am, don't jump down my throat please)
It's like, in order for me to play Metal Gear Solid 4, I HAVE to get the next gen system. I don't recall seeing games being made for past gen and current gen when it was Playstation 2 upgraded to 3, and Xbox upgraded to 360.
Now, we have it where companies are still making games for the old gen AND the new gen, which is putting people in a weird funk. It's either they wait and save while dealing with graphics and gameplay that's just for the PS3/360, or they spend for the next gen systems and stay up with what's current. We never really had this kind of a problem before, and now it's becoming a problem.
It's a problem obviously, because you have people who aren't getting the current systems for various reasons. And these gamers are most likely demanding that stuff still gets made for them so that they're not "missing out" on anything. (If that's the right term to use, forgive me, I'm currently unable to sleep right now and it's 1:15 in the morning)
We still have gamers who are using past gen and wanted this game to come out and still want to. I don't blame them. If I was in their shoes, I'd be bummed and pissed (not to a point where I'm going to stop supporting the series, but bummed to where I might not be satisfied with them for a long time) Would it be a little different had Netherrealm/Warner Brothers never made an announcement claiming that they were going to try to make this game for past gen? Possibly, you might have some people getting current gen systems just for this game and it's possible that some users here did that.
But, as I said before and as well as others, they've cancelled this and there's really nothing much else to add on. Making petitions won't work, I doubt they'll read fan mail... I guess sending angry Twitter messages might get through to them.
Who knows, maybe we'll get an answer during the next stream.