It seems it's much more common nowadays for people not to have seen the original trilogy; 10-15 years ago, I think it leaned much more in the opposite. After all, they're so thoroughly ingrained into American pop culture that it's impossible to escape their influence. Sometimes I felt like I had already watched the series via osmosis based on how much of it I'd seen parodied and referenced in numerous other movies, shows, games and music.
I just happened to be in a special position where it was inexcusable for me to have never seen Eps IV-VI. In addition to having seen most landmark sci-fi films from the '50s onwards, my lifelong venture into trashy cult films led me to see everything from 'Star Wars' rip-offs ('Battle Beyond the Stars', 'Star Crash', 'Spacehunter', etc.) to 'Star Wars' parodies ('Spaceballs', 'Galaxina', 'Ice Pirates', etc.) and even to other George Lucas films ('THX 1138', 'Willow', 'Howard the Duck', etc.), but just not the original trilogy. I never consciously avoided it, it's just that there were so, so many films on my specific radar of weird low-budget B-movies to get to that something as major as 'Star Wars' was as unlikely to cross my path as, say, 'Citizen Kane', which I didn't see until my twenties. Although, since I hang out with a lot of movie geeks, I always did get a mild thrill whenever they'd flip out over me never having seen the Holy Grail of movie geekdom.
Coincidentally, I happened to finally watch Episode IV today, albeit the "special edition" with its amazingly distracting CGI inserts. It's really quite astounding that the entirety of the original 1977 film has aged extraordinarily well, but the state-of-the-art computer graphics from 1997 have aged about as well as a glass of milk left sitting in the sunlight.
