...Well, okay, I'll grant you that. Blanket statements are always bad; only Sith deal in absolutes.
Grappling depends on size, strength, and base attack bonus. Xykon's size and base attack bonus are similar to Roy's at that time (if Roy was about 10th level, pure fighter, and Xykon a bit over 20th, pure sorcerer), and his strength is almost certainly lower. And there might be some circumstance bonuses involved. The frost giant's size is (of course) bigger, may have a higher Strength, and likely has comparable BAB.