I imagine these days more people are using Google Suggest. Therefore, whether you originally intended to search for "running shoe" or "running shoes," Google Suggest ends up dictating which term you actually search (at least that's been my experience).
On the other hand, not everyone uses Google Suggest, so I think the point made in the article about singular and plural queries is relevant. When I search for "mobile phone" and "mobile phones" on Google, without relying on Google Suggest, I get different results for each term (although a few websites appear in both results).