In a move similar to what they did with video view counts, YouTube has announced it’s going to start tightening up on the way it counts subscribers to any given channel.
The idea is to make the figures more accurate by removing suspended accounts from channel subscriber totals; makes sense since those people won’t be watching your videos anyway.
In the short term this could mean a cull in your channel’s Subscriber count but a more accurate figure has to be more pleasing for pedants and, more usefully, better for advertisers and therefore ultimately any revenue you might be making.
The change kicks in on June 16th and YouTube says it’ll be an ongoing process; it’s also reversible in the event of some dreadful error.
See their blog entry at http://youtubecreator.blogspot.co.uk/2014/06/making-sure-your-subscribers-count.html