It's because of that thread that people mistakenly believe you need a gmail.com address. A bunch of people in that thread guessed you needed a gmail.com address. Others immediately said no, you don't need it and showed examples.

But this is how misinformation spreads. Many people only read it and believe it without looking closer.

We just trust that other people know what they are talking about. :)

... Also I could be wrong, I'm trusting the counter examples in that thread. :D