"I just flew in from Europe -- and oy! are my arms tired!"
If you're still kicking around the issue, my two cents (and remember, the US Dollar is on a nosedive lately) is: folks are telling you to allow it since it's a FANTASY ... which is valid. But for myself personally, I'd still want to understand HOW the fantasy element works, and I think it's important that the READERS understand the "rules" by which your creatures operate (otherwise, it's just a jumble of unconnected images and deus ex machinas -- or is that the wrong plural?)
Do they have wings all the time? Because if they can suddenly materialize huge wings, why cannot they re-materialize themselves into a smaller package (the mind-image of a small creature flying doesn't bother me, but the image of a man with wings flapping across the Atlantic just strikes me as ... silly. That's JUST MY OPINION, what one reader might find silly, another will think is weird and surreal and absolutley wonderful! The witches on broomsticks in THE GOLDEN COMPASS struck me as silly too ... but obviously I'm disapproving of a huge bestseller!
My main point would be: remember that even Fantasy worlds have to run by consistent rules to satisfy the readers' expectations. Even if a creature COULD flap across the seas ... why wouldn't he just hop a jetliner to save himself the work?
I always liked how the vampires in THE LOST BOYS just floated around, it was eerie. Every reader has cultural expectations, and re-imagining things can be tricky. Vampires poofing into bats might remind someone of Abbot & Costello, some guy sprouting wings might reek of Superman.
Nothing can sound sillier -- or be more horrifying -- than blue flying monkeys in WIZARD OF OZ.