A bit minor, but it's a little surprising that Superman isn't spending his birthday with his parents.
Countered by Fridge Brilliance when you remember that Superman could easily spend part of the day with his parents and part of the day at the Fortress. It's not like he has a long commute.
In regards to the comic version, if we're talking about the Kents, it was Pre-Crisis on Infinite Earths. Jonathan and Martha Kent died shortly before Clark went to college Pre-Crisis.
And for the animated one, there's also the element of Fridge Brilliance that since the Black Mercy attacked Clark while he was in the Fortress, surrounded by memorabilia of his Kryptonian heritage, it's no wonder that he dreamt of life on Krypton.
So, why didn't Mongul kill Superman after using the black mercy on him, it seems pretty careless of him to assume that nobody would show up and remove it.
He propably did knew, but he just didn't care. I mean, he hardly came of as the most humble person ever, he propably just thought he would kick their asses and get a chance to talk about how clever he is.
Another possibility would for Mongul to keep Superman in his suspended happy land while he conquers the Earth, than bring Superman out of his happy world into a burning wasteland as a trophy, caught in despair for the two worlds he has lost.