That doesn't matter. If you want normal people to use Ubuntu, you don't start on at them about Unix conventions.
I'm pretty sure Ubuntu adoption rate isn't affected in the least regardless of whether you call it the Super key or Windows key, or Logo key, or any of the other names it's gotten over the years. "Normal people" don't ever use that key anyways.
2. It's not about adoption. It's about usability. Everyone will know what you mean if you call it 'the Windows key'. The same is not true if you call it 'the Super key'.