It's not really in character for Tywin Lannister to spare his second son any discomfort. However, he might have had an entirely different reason for abolishing Tyrion and Sansa's bedding ceremony. At Tywin's own bedding, Aerys "took certain liberties" with Tywin's beloved bride. Between Joffrey's general behavior and his intent to rape Sansa later in the night, Tywin might be seeing too much of Aerys in him.
