They talk about the reasoning behind it in their blogs on the site and it's interesting to see their take on confronting Google and Microsoft's Live search, and it's easy to see if you compare the results from all 3:
Search for Rio Tinto on Ask
Search for Rio Tinto on Google
Ask have gone for a much more intergrated approach - there are blogs, news stories, images, weather - even entries from Wikipedia. Interestingly, they have included related searches, based on the search patterns of others who have looked for the same thing.
This is pretty clever (well, I've always been easily impressed), but for us it's also a bit of a challenge. Potentially, if we have lots of activists or detractors searching for us, we'll start finding "anti-us" websites appearing more and more options, as their search patterns skew the results. Similarly, if there's a lot of anto company blogging going on, Ask are giving an nice easy way of presenting this to a wide audience, irrespective of its accuracy.
I can't see either Microsoft or Google hanging around after this, and it's probably only a matter of time before they too start aggregating search results in this way (to some degree, Live already does so).
This makes it even more important in the future to keep a close eye on your reputation online. You can't bury it anymore, or hope it'll just go away. It's out there, and it's gonna get you.