Ok, that's what I thought. It's technically better this way I guess. Designing the icons to work within our design and then linking them, as opposed to being stuck with whatever embedded options we'd have.
From my own forays in social buttons in emails. Be sure that you add the image in the email, from there you can embed a token into the link if you require multiple accounts, perhaps based on region. (We have a twitter feed per country) so every email I have has a twitter button, then in the link is a token for the twitter url.