Yahoo is adopting a strategy that it should have tried much earlier, turning its mail service into a platform upon which others can develop new applications. So, a third party could develop a new display for the email, build new features for it, or combine it with other applications. This makes sense for multiple reasons. Yahoo doesn't know exactly what will be a hit with consumers; it could put a lot of effort into one new system, only to see it be a dud. And by opening it up, it makes web mail more like regular email, which people can access using a variety of programs and services.
Very interesting, for more info read
http://techdirt.com/articles/20061002/081932.shtml
Regards,
Nikhil Kale