I noticed this as well. The older search results have the same width as the new results.
It's also interesting to note that the old results page is displaying multiple results for single domains using result nesting, while the new results page displays only one listing for each domain. The end result is that the same number of 'effective search results' are displayed on the page for both versions.
The gradual transformation of white space into content is a natural evolution in the life of any web product. While the feature set is simple, the design can be sparse. Mature products benefit from rich feature sets, with the drawback of having to sacrifice the sparse visual design that may have initially distinguished them from the competition.
I honestly thought about cutting all the white space completely, but then after having a chat with our designer... He said that every page is visually divided into blocks (even if there are no explicit visual borders of these blocks), subjectively, of course. This, the "F-pattern" and "left-to-right" orientation for the most of us brought us to an agreement that the last screen was ok... The subjective "blocks" are somewhat like this.
In the recent screen capture all the whitespace is added to the non-search results.
In the not-so-recent results there is a fair amount of whitespace added to the search results (as well as non-search).