We have allowed ourselves to be indoctrinated by consumer culture to where fancy china s seen as an appropriate gift, and a gift certificate is less so, but still acceptable, but many people consider a gift of cash to be tacky.
A pretty large number of stores have gift certificates that expire, or reduce in value gradually to nothing if not redeemed. A lot of them are never redeemed, which means you have given your wedding gift to the store and not the couple.
Wal*Mart at least sells certificates that never expire, and are good for something everyone uses: food. Naturally, there are many that would consider a non-expiring certificate to Wal*Mart more tacky that one to Bed, Bath and Beyond, where there is a far smaller selection, and at higher prices.