I recently spotted an extreme example of the popularity of the Slav and Semi-Slav variations. I was looking at Magnus Carlsen’s games with White after 1.d4 d5 2.c4. Now there are several solid moves (such as 2…e6 or 2…dxc4) and many off-beat lines (for example, 2…Nc6 or 2…e5) but between the start of 2008 and the 1st of June 2009 all of Carlsen’s opponents replied 2…c6. I make it about 18 2…c6’s in a row.
Elite chessplayers are dedicated followers of opening fashion.
John