Is It Necessary to Buy Both a Wedding Gift and a Shower Gift?
Here's the deal with wedding gifts: Technically, you aren't obligated to ever get a couple anything. If you do get them a gift, you're just expressing your goodwill and support of their marriage. That said, most to-be-weds and wedding guests alike consider wedding gifts pretty much obligatory.
Showers are somewhat different. The same rules apply, but since it's technically a gift-giving party, you'd likely be remiss to show up empty-handed unless the hosts have declared it a giftless shower—which are actually becoming more common. (That's why for years the etiquette was that no one in the bride's family could host the shower, since people perceived that as a greedy grab for additional wedding gifts.)
Nevertheless, bringing a gift to the shower doesn't technically constitute a "get-out-of-gift-free" pass for the wedding. That said, if you want to give the couple a gift at the shower but not at the wedding, that's your prerogative and you're not wrong for doing so. If you're worried you'll seem cheap with only one gift—which we certainly don't agree with, but we digress—the easiest solution is to simply split your gift-giving budget between the shower and the wedding rather than overextending your finances to buy two full-scale gifts.
Next time you're invited to a shower and wedding, use your own discretion. Either get a gift for one of the events, or a gift for both. It's totally up to you.