"Your name" isn't a required field and pressing Enter doesn't do that when the textarea is focused.
Additionally, not everyone knows that's the default behavior for pressing Enter in a text input and it's common for forms to be implemented in such a way that it doesn't work.
It would have been more semantic to use <em> for emphasized text instead of <I>.
Placeholders on form fields are not labels. The comment submit button has tabindex="-1", preventing keyboard users from submitting a comment.