Right, that's what I thought it should be like. Still not working, even in a fresh test scenario. Here the steps to follow through:

1. So I generate a new app using sencha app generate...
2. I add the following items to the sample view:
Code:
                {
                    xtype: 'filebutton',
                    text: 'File Button'
                },
                {
                    xtype: 'filefield',
                    fieldLabel: 'Photo',
                    labelWidth: 50,
                    buttonText: 'Select Photo...'
                }
3. Then I add these classes to Application.js
Code:
    requires: [
        'Ext.form.field.File',
        'Ext.form.field.FileButton'
    ],
4. Refresh or build
5. That's the result, because "x-form-file-input" is missing.
Screen Shot 2013-11-06 at 10.16.16 AM.png

Adding the class manually corrects the problem and I get this:
Screen Shot 2013-11-06 at 10.26.20 AM.png