The move is certainly a positive one as it means Google is being more transparent about its ads. That being said, the search giant is only making the change now because it is already dominating the search engine industry. Google purposefully used the less clear label earlier when its brand was much more fragile and the company didn't want to be associated with advertising on the frontend, even though that's what was driving its backend. For what it's worth, Bing currently calls the advertising section "Sponsored sites" while Yahoo uses the phrase "Sponsored results." The two may have to respond to Google's change at some point in the future.
PR business aside, it's possible that Google found the new label is better for click rates. It could also signal a strategy shift for the search giant: could the company be thinking of including advertising that isn't just links? Maybe image, video, or even map-based ads are on the drawing board.
"We are always experimenting with the look and feel of our search result pages, including the delivery of relevant advertising," the company said in a statement. "This is on English language domains now and rolling out to all languages and domains." The old label is still on all of Google's other properties.