The steelite of today is certainly NOT unbreakable, its certainly toughened to withstand a good clattering, but unbreakable it is not. try throwing a cup against the floor!
We use a lot of steelite in the hotel, and as l say, tough though it is, it will break if dropped on the floor, but putting a load through the dishwasher it will stand upto a lot of throwing about so to speak.
In the same token we have an unbreakable glass dance floor, no one has as yet tried to hit it with a sledge hammer to prove the point, but, we are assured it will stand such things .