When you buy a Giclée print of a digital work, you  have bought the original and unique physical copy of this Artwork, but the copyright of the digital image belongs to the artist. The artist reserve all the copyright rights for any use in an irrevocable way if not specified in writing.

The artist reserve the right to use the digital image in any electronic devices and for any use, and in general any other digital use, commercial or promotional, of the digital image. 

When you buy an Oil work, you own the original, but the artist reserve his copyright over the digital file for any electronic use.