So Gmail selectively catches the Wave?... Also see Google makes emails more dynamic with AMP for Email | TechCrunch
"Over the past decade, our web experiences have changed enormously—evolving from static flat content to interactive apps. Yet email has largely stayed the same with static messages that eventually go out of date, or are merely a springboard to accomplish a more complex task. If you want to take action, you usually have to click on a link, open a new tab and visit another website.Take action and stay up-to-date with dynamic email in Gmail | Google Keyword blog
Starting today, we’re making emails more useful and interactive in Gmail. Your emails can stay up to date so you’re always seeing the freshest information, like the latest comment threads and recommended jobs. With dynamic email, you can easily take action directly from within the message itself, like RSVP to an event, fill out a questionnaire, browse a catalog or respond to a comment.
Take commenting in Google Docs, for example. Instead of receiving individual email notifications when someone mentions you in a comment, now, you’ll see an up-to-date thread in Gmail where you can easily reply or resolve the comment, right from within the message."