Is it? Don't know yet. I am running an affiliate site and if your words turn true it is really a worry for us.
I read they banned 30k affiliates a few years ago and they also shut down the Google Affiliate Network. But they still view amazon product reviews and affiliate links so it's only a worry for spammers imo. Maybe Google is just trying to clean it up and only allow real sites to appear in the top search rankings.
Actually its correct. Google doesn't downgrades affiliate sites but since they are lot of marketers who try to spam to get ranked and sales by buying fake reviews or some such sort. So, every now and then google filters out the good sites from bad ones.
Google may decrease ranking of affiliate sites which are not providing any kind of good content, will not get ranking for informative search queries.
Google looks for sites that are "thin content sites" and may 'penalize' them. Best practice is to minimize the number of the outgoing links and add lots of valuable content. If you have an affiliate store, put it in its own subdomain or directory.