This is not just ugly and confusing from a marketing and branding perspective, it leads to all kinds of complications with software that reacts to email-addresses, or services that are coupled to Google Apps.
We have one primary domain and 15 alias domains. Email Example: [email protected] gets an email, when they reply it stays set to the alias, it doesn't change to the primary domain.
According to Google, they don't include this header if you upgrade to Google Apps for Business.
Until they decide--all of the sudden--that you can't any more (assuming you can now). His point is that Google is unreliable as a long term partner and should not be counted on.
I have not found anything on such a migration path so far, only more or less desperate forum posts …
Google Apps also have the advantage that you can mix free and paid accounts. We have for example some employees who share their business calendars (paid accounts) with their family members (free accounts).
As much as I dislike everything Microsoft, 365 currently looks well ahead of Google (everything they haven't killed yet has definitely stopped evolving), and has certainly proven to be a more reliable partner for business use.