The shortcuts from settings only applies to the main QGIS window. Other windows (i.e. the attribute table) have their own shortcuts assigned. I don't think this can be changed from the GUI but you can using a bit of Python.
Load the attribute table(s) and then open up the Python Console from the main QGIS window (Ctrl + P). Then use something like the following:
from PyQt4.QtGui import QApplication, QKeySequence
from PyQt4.QtCore import Qt
attrTables = [d for d in QApplication.instance().allWidgets() if d.objectName() == u'QgsAttributeTableDialog' or d.objectName() == u'AttributeTable' ]
for tables in attrTables:
for x in tables.children():
if x.objectName() == 'mActionZoomMapToSelectedRows':
x.setToolTip('Zoom map to the selected rows (Q)')
Now you should be able to zoom to the selected feature using Q.
Note: this will no longer work if the attribute table is closed.