Don't worry too much about high grade boundaries on some of your exams guys.
They change them according to the difficulty of the paper and how students performed on the exam. They try and keep it so roughly the same proportion of students each year will get a certain grade, so if you've been getting A*'s in Maths papers, you should get an A* this time round.
With Edexcel, as well, with my GCSE's and AS levels I've always found the marks to be fair and actually postitive: examiners do their best to credit your answers and award you rather than penalise you which may lead to you doing better than expected.
As @usycool said, I've always preffered more challenging exams: you always do better than you thought you did, and often silly mistakes don't have such a big impact on your overall grade.