Well. As the tables were either glass or marble, I guess they were super flat.
... It is just strange that three different tables show exactly the same behaviour.
In the picture in your first post, the lid is not fully open.The thing is that I only observe this when the LID is fully open.
...It's not your table. I guess people on here think that metal is more difficult to bend than marble or glass. its not about the table being level, its an uneven surface, which isn't likely.
OP: It's not horribly uncommon, but it's not really a big deal either unless the movement annoys you. If it does, matchbook? lol