Floppy ears doesn't relate to any health issues. Or at least I haven't heard otherwise.
Have you seen their parents? What your mom said is partially true. Shaving the top of the ears help with lessening the weight so it helps their ears get perky. Also, being puppies, a lot of the calcium in their body is probably focusing on going towards their teeth rather than their ears.
I think floppy ears are just adorable!