That said, if I change the call to this, dpm($variables['classes']); I get this output:
... (Array, 0 elements)
$...
Krumo version 0.2.1a | http://krumo.sourceforge.net Called from /home/quantate/staging/sites/all/themes/genesis/genesis/template.php, line 152
... (Array, 1 element)
0 (Array, 1 element)
Krumo version 0.2.1a | http://krumo.sourceforge.net Called from /home/quantate/staging/sites/all/themes/genesis/genesis/template.php, line 152