Time To End The Bullshit Search Engine Share Figures? by Danny Sullivan is a must read for anyone interested in how search market share statistics work.
In summary, Yahoo, after months and months of search market share decline, is now seeing a few months of search market share growth. Danny basically says that Yahoo, like other search players, game the system. How? Well, Danny digs into how in his article, so check it out.
This is nothing new, search engines and publishers have done this for years. It is a numbers game. For search market share, it is about the number of queries. If you can get more queries, you get more share - even if they aren't hand entered. Publishers want more page impressions, if that means you paginate articles or drive interest to click on related articles or other methods, that is how publishers monetize their sites.
Yes, this is nothing new. But the statistics we use to measure a site's value has not changed much. Yes, we have new metrics, like "engagement" and so on, but they aren't used for selling ads.
This is an issue where I really see no solution to in the immediate future.