In actual fact the dropping of the 'e'didn't happen always happen in the US.
The spelling on the Parish Records (for Elmdon and Langley, Essex, UK) spells it in a variety of ways eg Wisby Wisbey Whisby Whisbey. I expect it all depended on the Vicar, or whoever wrote up the records,and how he felt it should be spelt. It is apparant from the PRs that most of the Wisbys, Wisbeys, etc could not write as they signed with Xs so they could not tell the Vicar if it was spelled wrongly.
As far as I know my Wisbys remained in England but I could be wrong as I really only know for certain that Sophia died here in Essex (at Rayleigh).