The reason tri-lobe screws are used is because a Torx drive socket on a screw that small wouldn't work. The tri-lobe is like a Torx profile and has the same advantages, but with two less lobes. In addition, tri-lobes are used because it can be put on a screw with a thinner head, where other drive types wouldn't work. The thinnest screw heads (0.3mm and below) require tri-lobe.
Do people really think nefarious apple engineers are intentionally trying to keep users from doing repairs? They could care less. Besides, if anyone's gotten that far, a screw type with an uncommon head is not going to stop them.