There is the rather delicate issue of copyright here. If you google for something and the answer is on another page, lifting it from that page is (a) making a copy and (b) potentially depriving the linked page of revenue.
There is also the question of using the threat to ban people from your search results (which is calamitous for most businesses) to resolve your disputes with them.
But the linked page is there. Google is indexing Amazon, extracting the photo, description, and price of the product, displaying it in a box, and making it a link back to Amazon where it got the data from, what's the problem?
Product Search is just another form of summarization/snippeting that just presents the data in more digestable format.
Remember Google Fusion Tables? That was an attempt to extract facts from pages and put them into tables, so if you ask "What's the masses of the planets of the solar system", you could get a table of 8 planets and masses, with the results coming from 8 different sites. But the links could still be there to the original site, it's just formatted as a table instead of as 8 blue links with summary paragraphs, which is harder for humans to process.
Now what if this same system eventually allows the search engine to summarize your web page by 'reading it', and then auto-generating a paragraph that explains what it thought it was about?
There'd be no actual direct copying of text (like there is with search snippets), instead it would be more like a human going to a library, reading a book, and writing a review
That question is moot in the shopping context; the products that show up in that system are fed directly to Google by the owners of the product listings.
There is also the question of using the threat to ban people from your search results (which is calamitous for most businesses) to resolve your disputes with them.