Emails are often sent in batches and when you have an enormous customer list (which BAC does) it can be difficult or impractical to send to everyone at the same time. And even if you send together, doesn't mean they'll be received together. I wouldn't be too concerned about this personally.

As for 'leaking' to the press, normally PRs for significant/confidential news will be sent ahead of time under embargo. This gives the press the time to write about it for when it comes out. Though as this particular change was relatively minor, it probably wasn't embargoed anyway and just communicated in one.