Noted in an official blog post
earlier this week, search engine giant Google is altering its search algorithm to better address the current needs of smartphone and other mobile device users. Most notably, the search engine is downranking incidents of faulty or irrelevant redirects to a site's homepage when a mobile user is clicking through to seek specific content.
Additionally, Google is also downranking incorrect handling of Googlebot-Mobile, Google's crawler for mobile-specific content, incidents of unplayable videos on mobile devices specifically noting Flash videos on Apple's iOS, and problems with a smartphone-friendly landing page identified as a 404 or other error page. The change is intended to put pressure on websites to ensure modern, standards-compliant designs, but may also have the effect of pressuring operators to customize pages for Googlebot-Mobile rather than focusing equally on all search engines.
The blog post says that "avoiding irrelevant redirects is very easy: simply redirect smartphone users from a desktop page to its equivalent smartphone-optimized page. If the content doesn't exist in a smartphone-friendly format, showing the desktop content is better than redirecting to an irrelevant page."