To me you haven't made any case at all why others should have to suffer so you can have auto-focus on Amazon when your needs are already met elsewhere.
"!amazon thingamabob" (or just "!a thingamabob").
Way more convenient than going to the homepage and worrying about search auto-focus.
"a foo" to search on amazon, "g foo" google, "i foo" imdb, "m foo" google maps, "w foo" wikipedia, "u foo" urbandictionary, etc... I have more but they are not public sites.
Sounds like the two could complement each other, like aliases and completion in a shell.
I have "w" for wikipedia, "y" for youtube, "gm" for google maps, etc...
This is THE feature of Chrome that I use constantly every day. It saves 5-10 seconds on each search you do every day. It adds up.