I spent half a year being charged monthly by Microsoft because Google considers my email address the same whether or not it has a period in it but Microsoft had somehow split my account into two based on that difference.
that's.. really on you I think, and not at all similar to one site having differing validation rules in different places for the same data. What gmail does there isn't some kind of standard, it's a unique special feature google does. You don't want other sites getting clever about this sort of thing, because if the rules change much worse things will happen.
Now, sites that treat email addresses as case sensitive - those are evil.
Xbox Live Gold. I'd call, give them my account details, and the rep would tell me it was canceled. Three months later, another bill. Called my bank and had my card replaced, three months later somehow again another bill on my new card. After that I figured out what was going on and managed to cancel the account. I was a teenager at the time.
