Ubuntu is not "selling" your searches to amazon. Ubuntu will only get paid any money if you click through, and purchase something from Amazon. Ubuntu is sending your searches to Amazon which may or may not be 'right', but they only get paid if you buy stuff.
I'd guess Ubuntu are desperate for revenue and have run out of other ideas.
Also FWIW, the number of people who use these desktop search things seems likely to be tiny. Particularly amongst those who use linux.
Do people here use desktop search on any OS?