Steam store "refresh" is out in beta now, enwidening images and adding infinite scrollage to the homepage
(www.rockpapershotgun.com)
You can.
Open a publisher page, then in the top right corner, look for a gear icon. Click it, and there's an option to ignore this publisher.
Unfortunately there's a limitation. This works only for those having a dedicated publisher page. For publishers without a dedicated page, Steam will fallback to the search page, which doesn't provide a way to ignore this publisher.