1.They have more money than (is) necessary/expected.这句话省略is是特殊例子吗? 与The medicine is more effective than (is) necessary/expected的省略是一个原理吗？还是说第二个句子是省略与前面相同的is? 
2.There are more potential problems exist than is the case.
这句话中than is the case中如果改成cases可不可以省略be动词（就像1中的第二个句子一样）？换句话说，比较状语从句中be动词和助动词如果和前面的重复了，但形式不同(有的是三单有的不是)，可以省略吗？就像如下两个句子中的You are more diligent than Bob (is). She does more work than they (do).