yeah, an issue with the SQL statement.
Since it's in a file geodatabase, could you just use the Null value approach?
import arcpy
fc = r"C:\tmp\Test.gdb\WCSCustomer"
field = "GROUTE"
whereClause = field + " IS NULL"
updCurs = arcpy.UpdateCursor(fc, whereClause)
for row in updCurs:
if not row.getValue(field):
updCurs.deleteRow(row)
Or use Mitch's example of if x is none, etc....