Why does Spike use digital keyboards in place of acoustic pianos?

I don't think Paul Mccartney plays a grand piano on his recent tours. When I saw him in Arnhem in 2003 he had an upright one, with very cool decorations

I saw spike playing with the BMB (The brian may band, of course!)on the another word tour but i'm not sure to remember wether he was actually playing a "real" piano (could it have been some sort of vintage organ?) or a keyboard device fixed in a wooden furniture. I do recall it gave me a "retro" impression.