This is good news because it's not great to have all your eggs in one basket. Depending solely on traffic from this one source is not good for a website. You can do months of work to get it on the top of page one for a particular keyword search and then lose that position in an instant when Google decides to tweak its algorithms. This would be a hugely negative outcome for obvious reasons. But merely worrying that such a thing might occur can cause a lot of anxiety as well.
The fact that there are now more search engine possibilities is yet another reason why blogging is such a good thing to do. Google traffic is desirable, of course. So you should use its keyword tool and the drop down suggestion box to get ideas for blog posts. But if your post fails to rank highly there as hoped then there's still a good chance it will do so on Yahoo and Bing, which use different algorithms. That's a comforting thought and makes blogging all the more worthwhile.
For the same reason it's a good idea to get visitors from social media as well -- not to mention offline sources and pay per click. Spread your traffic sources around and you can make sure that the money you earn from your website is coming in more consistently.