I think there's an important difference between "Immobilized" and "restrained"
Restrained is like a worse immobilized. Tha DOES make you easier to hit (combat advantage), while Immobilized means you can't move from your current 5-ft square. 5 feet is a lot of space, so it may help if you imagine something that would just keep you from moving outside of that.
Legs going numb from a ghoul's attack is a good example. You can still shuffle around within that square, you just can't make any appreciable progress other than that. For the ice, I'd say just one foot gets caught, or perhaps your cloak, or something similar. You can keep fighting, just have to keep that foot planted.
Restrained is like a worse immobilized. Tha DOES make you easier to hit (combat advantage), while Immobilized means you can't move from your current 5-ft square. 5 feet is a lot of space, so it may help if you imagine something that would just keep you from moving outside of that.
Legs going numb from a ghoul's attack is a good example. You can still shuffle around within that square, you just can't make any appreciable progress other than that. For the ice, I'd say just one foot gets caught, or perhaps your cloak, or something similar. You can keep fighting, just have to keep that foot planted.