Etiquette or not - I do not always give gifts when I attend a wedding, and when I got married, I invited many people from whom I expected nothing but their presence at my wedding - to share my happiness.
I've gotten baby shower invites that specified that a certain color was not to be given - if a person is that picky, I just don't give anything.
In general, actually, I give gifts when I can AND want to. If I get an invite from someone I am only marginally acquainted with, I generally RSVP that I will not attend, and then I don't think another thing about it. I really dislike the trend of inviting people to things just so that they'll be aware that a gift giving "opportunity" is at hand.