They could be photos from when The Queen Mother lived there, though I imagine not all photos are the same age.?
Clarence House is the residence of Charles and Camilla.
I like that it is full of memorabilia. It looks lived in - with the paintings hung low - it's more homely.
St James Palace, while being perfect for a reception area and business meetings, appears cold and stark to me. Public spaces need to be uncluttered where-as a home can afford a more unfashionable personality.
The Cambridges will move into Princess Margaret's refurbished apartment in Kensington Palace but I think that their offices are now in St James Palace.