I agree to some extent, for example, in Geography. You need 75/120 to get an A. 45 Marks can be lost, and you still receive an A! However, I guess that makes sense since Geography is an essay based subject.
To be honest, to get my AS-level grades, I needed to work pretty damn hard, especially in Geography. So, I think that it really does depend on the subject. The exams are made to challenge you, but are also 'do-able'. So, maybe you have just mastered A-level exams.