No one arrives at any design independently. Design decisions are always informed by what's been proven successful, whether be the current designer or their competitors.

Apple has of course influenced the market. The question is whether Apple has the right to be only company in the market to sell certain things, like rectangular touchscreen tablet devices. I don't think they have that right.

I'm offended that anybody can look at the situation and argue Apple designed the iPad independently.

Would it feel better for you if the slot was only 19mm wide instead of 21?