It is very common to need to compare the values in two nullable columns, without changing the ansi nulls setting. For example, it is common to have to write:
WHERE (a.SomeColumn IS NULL AND b.SomeColumn IS NULL) OR (a.SomeColumn = b.SomeColumn)
Given how common this is (particularly for some forms of optimistic concurrency checks that aren't based on rowversions), there should be a simple way to express the intent. I also presume the optimizer could also potentially take advantage of knowing the real intent of the statement.