The label omission caught my eye as well, as that's a weak point of currently available iOS apps (official Gmail app being the best).
I use labels a lot, but not only for importance/order of dealing with things – I use them to categorize/filter out of inbox as well. Which then, yes I do apply importance to (I have a few minutes, let me look through these promo emails or all these emails from basecamp).
So basically I use the labels to do "bulk importance labeling", but I wouldn't want to auto-tag all those "holiday sale" emails to "Later", and then just have to deal with them again later.
Your usage description ("Instead of fooling yourself into thinking you’ll tackle this today, simply mark it to reappear tomorrow or next week – when you’ll actually respond.") sounds like it's only talking about person-to-person needs-action types of emails. I think myself and many other people have a wider range of usage for email.
BUT that certainly doesn't mean Gmail's label approach is the only solution. But for people currently using labels a lot in Gmail, strong support for that paradigm is nice.