Screws are much more delicate than glass. Screws strip very easily, making it impossible to remove the connection.
Most other drives don't have most of these problems. Even with the infamous Pentalobe, as long as you get the size right, it's pretty hard to screw up.
edit: Apocryphally by design, anyway. Wikipedia says that's an urban legend, unfounded. I cordially despise the things either way, and I'm sure the sentiment is reciprocated.