Well I looked up sachertorte on wikipedia and it mentioned some people make it with margarine. To me that is... it's just... no. In desserts one should always use butter, not margarine. Margarine might be unnoticeable in some dishes, but the dessert is made specifically for enjoyment.
That's one thing I have against Pepperidge Farm and all their little bags of cookies. They don't make them with butter, they make them with vegetable oil. If only they would use real butter, those things would be wonderful.