My only real concern with the type-size adjust tools being integrated into the page are when they come at the expense of the built-in browser tools.
I’ll agree that many (perhaps most) users have no knowledge of the these tools. I’d argue, however, that there is a large, specific contingent that do. For those, performing the same task on every site (using the built in browser resize) is better for experience.
That isn’t to say that the on-page tools don’t have a place, but as a sight-impaired user, I’d hate to have to hunt around every site I visit, looking for their text-adjust implementation.
@Nathan Ziarek: I couldn’t agree more. What really annoys me with sites that have these font-size selectors is, that at no point I can return to the default. After I’ve played around with the up and down for a while, I’d like to see how the website was intended to be shown. I can easily do so with the built-in browser tools.