For the RadSpreadsheet control, the key bindings are kept in the InputBindings collection of the RadWorksheetEditor, instead of that of RadSpreadsheet. The following line should do the trick:
.radSpreadsheet.ActiveWorksheetEditor.KeyBindings.RegisterCommand(myCommand, Key.S, ModifierKeys.Control);
Let me know if you need anything further regarding this or any other matter.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items