For the benefit of others who may come across this thread while searching for a solution to the problem described at the top, here's some additional information.
As of late Oct'13, Pages V4 (which was part of iWorks '09) is not advertised on the App Store. Apple has pulled it, and posted Pages V5.0 in its place. According to the App Store listing, OS X 10.9 or later is required to run Pages V5.
If you connect to the App Store using 10.6.8 (Snow Leopard) and attempt to download Pages, an error ensues:
Pages can't be installed because Mac OS X version 10.9 or later is required.
This error message is not correct.
If you connect to the App Store using 10.8.5 (Mountain Lion), the App Store thoughtfully responds:
Sorry, you need a later version of OS X for this application. However, we'll be happy to download a previous compatible version for you.
It then downloads Page V4.3, which runs just fine on ML.
I have found that Apple's Customer Service representatives are misinformed. In the last week, I was told on several occasions, by different Apple employees, that Pages V4 was no longer available from Apple, could not be downloaded from the App Store, and that the App Store can only 'stock' a single version (i.e., the most recent). In fact, the App Store does maintain inventory of multiple versions (at least two in this case, 4.3 and 5.0).
The message that "Pages can't be installed because 10.9 is required" is false. Based on my experiments, the App Store can and will install Pages V4.3 on Mountain Lion, and also on Lion (10.7.4 or later).
Unfortunately for me, V4.3 seems to require at least 10.7.4. It won't run on 10.6.8. My old MacBook Air (1,1) can't go beyond Snow Leopard, so I'm still up the creek without a page to paddle. I'm waiting for delivery of an iWorks '09 install DVD in order to get Pages installed on my MacBook Air. It's my understanding that the DVD contains Pages 4.0.