This works for me:
Qt Code: 
  1. #include <QApplication>
  2. #include <QTableView>
  3. #include <QStandardItemModel>
  4. #include <QScrollBar>
  5.  
  6. class WideScrollBar: public QScrollBar
  7. {
  8. public:
  9.     WideScrollBar(QWidget *p = 0): QScrollBar(p)
  10.     {
  11.         setStyleSheet( "QScrollBar:vertical { width: 25px; } ");
  12.     }
  13. };
  14.  
  15.  
  16. int main(int argc, char *argv[])
  17. {
  18.     QApplication app(argc, argv);
  19.  
  20.     QStandardItemModel model(50, 3);
  21.     for (int i = 0; i < model.rowCount(); ++i) {
  22.         for (int j = 0; j < model.columnCount(); ++j) {
  23.             QStandardItem *item = new QStandardItem(QString("%1, %2").arg(i).arg(j));
  24.             model.setItem(i, j, item);
  25.         }
  26.     }
  27.  
  28.     QTableView view;
  29.     view.setModel(&model);
  30.     view.setVerticalScrollBar(new WideScrollBar(&view));
  31.     view.show();
  32.  
  33.     return app.exec();
  34. }
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and produces a customised scroll bar that works as expected. If the table had only one row I would not expect to see a vertical scroll bar at all.