Although its more than a year since your contribution, I thought you might be amused to know that it is not just that the screws go in more easily when at an angle, Apple actually drilled and tapped the holes at a 15% angle. I too had tried to drive them in straight. An Apple "genius" - I was in for something else - clarified the design for me. It was done so that the screws lay flush on the angled part of the lower case. Nice design, but since Apple encourages DIY memory and drive changes, they could have mentioned this little ... trap.