I feel like I've only listened to Stairway to Heaven twice in my life. Part of that might be because, like you, it doesn't engage me. So, I may have heard it in other media or maybe even on the radio before but I find it unmemorable and simple so it doesn't stick in my head nor would I seek out on hearing it again. I just know that I've tried a couple times to listen to it all the way through to make sure I wasn't missing something and it just doesn't stick with me.
As far as Led Zeppelin in general, the only songs I'm somewhat familiar with are Kashmir and Black Dog. Even then, I think it is more from those songs being sampled in other media than from actually listening to them. I find Zeppelin seems to work better when it is just being sampled like that.