This is paltry nonsense. Gmail and similar host users are used to treating the dots as decorative, and will register with john.smith@ then try to use "Forgot username?" with johnsmith@ instead. They'll end up with three GitHub accounts registered to the same mailbox and be confused as heck about how they're still getting email notifications for an account that they can't recover a password for.

You can't break user expectations and mental models by pointing to the spec as justification. The spec exists to serve users, not the other way around.