They can and DO still happen, whether you save it for marriage or not.
Waiting until you're married for other reasons are fine….but I don't get why people give "no STDs" or "no unwanted pregnancies" as a reason.
Because everyone thinks that marriage is a contract to breed. So if you get married you obviously want to breed. Not to mention everyone assumes that all couples faithfully practice monogamy! Both complete crap and very untrue the world over.