I acknowledge the difference, but would counter that Visual Studio 2015, TextPad, and just for fun Word 2010 don't offer such options in their context menus. What the first two do have is increase/decrease line indent items in their Edit menus, and TextPad even has Ctrl-<> listed as alternatives to Tab/Shift-Tab. Seems a bit weird to have both.
Another thing to consider is that the Edit menu in SCI Companion works for almost every resource editor that has selection support. Indenting lines would need to be available only for the script editor, and does not feature what's in the script editor's context menu. This may be specifically because Edit applies to all. (I'll also note that "Select All" is grayed out in the script editor, but Ctrl-A works fine.)
A good UI would have context menu items be a subset of the main menu items. SCI Companion's script editor's context menu has unique items. And given it's an MFC project I'm in no hurry to correct that.