I can't comment on showers because we don't do those in the UK. Or at least, maybe they have come in recently but I have never been to one. If I was invited to a wedding and couldn't go, I wouldn't send a gift unless it was close family or a close friend.
It still rankles that we DID send a gift from my cousin's registry when they had a destination wedding with nobody present, followed by a party when they got home, which we couldn't go to. And we never got a thank you or even an acknowledgement. That was 3 years ago and they've just split up.
It's amazing the resentment that builds up over that kind of silliness, isn't it? There's nothing like bad manners for causing resentment.