The difference is important...
Viserys loved Aemma, and they immediately told him he had to choose "to sacrifice one, or to lose them both", so yes, he wanted to at least try to save their son... something he can cherish for his end days... but alas, the babe died.
Daemon doesn't love Laena... hell, he doesn't even love his children... they are all pawns, tools, meant to further his coffers. If the mother can live, save her, so she can produce more children, cause more children means more dragons... once she dies, she can't be of any use. He doesn't care if the child lives... but they didn't get a chance to even give the odds of her survival, she already had left to die by dragon fire.
I can see the parallels, indeed, but the reasoning behind each is important.