what should be clear is that there are bluetooth keyboards that implement 'functions' (fn key) related to iOS operations (volume up, down etc) and there are command keys that are implemented by the OS and have nothing to do with being implemented by the keyboard or not...
so some shortcuts or buttons on a keyboard (bluetooth or not) can be implemented by it's manufacturer, while other are 'standard'. correct me if i'm wrong, but unless your computer's driver is messed up AND unless you connect a keyboard that sends the letter 'w' when you press the letter 'e', when you press the letter 'e' on a standard keyboard, the computer displays it no matter what brand of keyboard you are using...
and if a logitech or any brand keyboard manufacturer makes a button that does a special function, until the keyboard driver is installed, it will never work, but when you press a letter button, the default keyboard driver will display the letter you pressed..
my whole point is that if an app manufacturer makes the app do something when you press cmd-something, the keyboard manuf. does not need to do anything special... other than 'implement' a standard cmd key...
as far as the spell checking not working in apple's 'pages', i don't think it's a logitech keyboard issue.. as it does the same problem when bluetooth is off, using the iPad's screen keyboard.