By definition, 'what you wish the iPad to have that it does not have' equals 'what the iPad is missing'.

If I expected it to operate as a razor and it could not while other similar devices did have that feature, then yes, I would say shaving capability was missing. That doesn't mean every irrelevant concept I can come up with would be called missing, though. 'Missing' is based on what one would expect, desire and can get elsewhere.