I've looked at the Clewer parish records (Berks FHS CD) and Henry and Hannah Newton were witnesses to a marriage (William Billings to Charlotte Bennett) which took place there June 21 1816 - so only 3 months after the Henry Newton/Sarah marriage in Windsor. I suppose its not impossible Sarah could have died and he remarried to Hannah within 3 months, but perhaps not very likely?
I can't see a burial for a Sarah Newton in that short time on the Berkshire Burial CD (Berks FHS again).
According to the 1819 baptism for Henry junior, his father was a servant at the horse barracks. Henry & Hannah had a daughter Hannah baptised in Clewer in 1824 when Henry is described as living at Clewer Green, pvte Royal Rgt Blues.
Just to make life more interesting (!) there is also a burial in Clewer for a Sarah Newton on 7 April 1809 - the entry says she was 31 years old and 'found murdered at home'.
Too early to be Henry's first wife but perhaps a relative of Henry's? I would think it would have been mentioned in the newspapers of the time.
Of course, Henry may have had no prior attachment to the area and, with him being a soldier, he may have been stationed elsewhere when he married Hannah. Do they appear on any later censuses which would give a clue to Hannah's birthplace?
Jill