I went with not moral, but it's really 'mostly no'.
That is: if you buy it, I see it as morally acceptable if you pirate it for other platforms or emulate it. I don't think it's fair to expect companies/developers to port their games to every platform or maintain it forever. If you buy it, it's yours (imho).
Piracy isn't stealing to me since it's making copies. But even so: the moral right thing to do is meet what the devs want, providing it's reasonable. If they sell it for platform X, buy it for X (even if you play it on Y). If they choose not to sell it anymore and don't label it abandonware, that's also a choice. We have to be reason able as well: do we REALLY want this game, or are we looking to get something for free?
A few caveats:
1. I'm taking morally here, not legal
2.abandonware is a huge Grey area since it often has to be agreed on by everyone, and studio's might not be around for that.
3.yes, I pirate. I have my reasons, but pretending it's a morally correct thing isn't among those reasons
4. Lots of yes votes, but... Sorry, but there's remarkably poor reasoning in the replies.