Google's policies regarding paid links have created a bias in the search results for a long time, and I have written previous articles over the last few years that explain exactly why this is in detail. Basically many webmasters including me, put nofollow tags on links that really should be follow links, and a large percentage of other webmasters I know also do this.
Because Google makes many mistakes and people are correctly afraid that the Google "Spam Police" will make a mistake and unfairly penalize them. So what is the safest solution?
Make almost all outbound links nofollow.
Does this have an effect on the Google search results?
I do not know the answer; I theorize that it may cause some negative long term impact on the quality of Google's search results. I believe it would be a very interesting test for Google to create a separate database (index) and turn off all nofollow filters, then have expert 3rd party Internet searchers compare the two different sets of search results and see which one is superior. You need really smart and advanced searchers to do this properly.