From the Google adwords Blog
Why are we doing this? Simply stated, we always aim to improve our users' experience so that these users (your potential customers) will continue to trust and value AdWords ads. Have you ever searched on a keyword, found an ad that seemed to be exactly what you wanted, and then clicked on it only to find a site that had little to do with what you were searching for? It's not a great experience.So basically, the rates for the key words bidding are going to depend on a combination of quality score and the quality of the landing page. Websites that have content or products to sell will find it bit cheaper to bid for relevant adwords, whereas website which do nothing other than redirect links will find it a bit more expensive to bid for these adwords. This will help improve the user experience about relevancy of the adLinks and save them from the frustration they currently undergo when click on an advertisement basically leads them to a links-farm. Google is going to evaluate the quality of the landing page and mentioned some guidelines which the websites can follow while creating these landing pages.
Incorporating landing page assessment into the Quality Score will help us improve the overall advertising experience for users, advertisers and partners by increasing the quality of the sites we present in our ad results.