Apparently it has to do with the fact that our Add to Cart button code for products using Variants/Variations submits the buyer-selected menu/field values via an HTML form, and Google Sites don't allow HTML forms to be pasted directly into the page itself, so they automatically embed any form code into an iframe in the page using a Google Gadget, which gets blocked if the buyer has blocked or disabled javascript in their browser.
Google Sites are pretty severely restricted in what they will allow, apparently with the aim of being foolproof, but that means even advanced users aren't allowed do anything they wouldn't also allow any fool to do, which includes adding forms for some reason.
Aside from simply accepting that buyers who block javascript will be unable to order from your page, and maybe putting a notice on your pages advising that javascript must be enabled to place orders, there is a way you could turn the Variants menus into a series of separate Add to Cart buttons, although this would not allow buyers to enter any information in a text field (which does require the HTML-form approach):
http://www.e-junkie.com/ej/tips.variants.button-tutorial.htm
