I grew up hearing that if someone receives an invitation to a bridal shower or wedding and can not attend that they should send a gift anyway. My family always adhered to this edict (probably by Emily Post) and the gifts went out. It wasn't until I married my husband 34 years ago that I ran into his family and their way of doing things. They absolutely do not send a gift if they are not coming. However I still do send one. I usually skip the showers but I always send a gift. My husband and I have never skipped a wedding ( I believe we have attended about 20 in the last 34 years) and, of course, we either send or take a gift.
If someone takes the time to think of us and to send us an invitation, I believe that we should honor them and either send or take a gift.