From comments on Gizmodo:
http://www.newtonphysics.on.ca/anomalous/index.html
“Published: 12:01AM GMT 10 Feb 2002”
“This article is from 2002. In the 8 years since this article was first published, scientists have discovered that Pioneer is colliding with space dust in the Kuiper belt, which slows it down.”
http://gizmodo.com/5642007/a-mysterious-force-is-pulling-pioneer-10-back-toward-the-sun
OK, knew about that, thought this was some new discovery.