They can certainly still leak, but the consequences are different. Instead of getting wet and risking water damage you have to sweep and vacuum wheat (or in my case rice) out of everything. Still, much less harmful to electronics and wood floors.
I forgot about this until now - when I was a kid we had a block of cement, basically a patio stone, sitting on top of the woodstove. When I went to bed, since my room was unheated, I would wrap the cement block in cloth and put it by my feet in bed. I kind of miss that cozy feeling, but then at the same time I don't miss how cold the rest of the room was. If I woke up to a 50 degree room now I'd probably never want to get out of bed!