iWork '09 won't update under Yosemite

I just updated my Mac Pro from Mountain Lion to Yosemite. I expected to see the new, Yosemite versions of Pages, Keynote and Numbers appear in the Mac App store under Yosemite, but instead, I see an "Open" button, not a "Download" button, and when I press it, the old, iWork '09 versions open. Similarly, when I search for "Pages" in the "Featured" page, I get an "Open" button, not a "Download" or even a "Buy" button.

How can I get the new versions?