Rockmelt has (had) a very strong leadership team (founders were very successful in the 90s), and a number of strong engineers.

It seems clear that this is an acquisition for talent, since they're shutting the product down with less than 30 days' notice.

For <$70MM, that could be a relatively cheap acquisition of talent that has proven their ability to make things (if not necessarily proven their ability to make a product that people want to buy - which is where Yahoo's responsibility and vision come into play).