I ahve purchased the above trees and have found that the leaves have fallen off, as a non gardener, is this usual and willl they be ok to plant outside in the spring?

Japanese maples are deciduous- they lose their leaves in fall/winter.

Yep, that's what I would have said as well...
Their leaves aren't meant to stay out all winter..
They change super colors, depending on the kind/variety you get and then fall off in the fall time and re~bud in the spring..

Those are beautiful trees....
What kind did you get???

Question here though????
Where are they right now???
And when is your winter???