But more to the point, Stallman does not just want open-source software. He wants free software, and just based on my informal observations, his ideas of free software seem to be losing traction these days. Yeah, there's a lot of open-source software, but BSD, Apache, MIT and other open-source-but-not-free licenses are taking the lion's share.
Even among projects that do use GPL, they mostly seem to prefer v2 rather than the more-free GPL3 and AGPL.
He thinks the Open Source movement misses the point, but he has no problems accepting their software as Free.