I think the one year with no serious damage guideline is very safe. With a friction saver, ropes don't pick nearly as much and probably last at least half again as long. The way my luck goes though, I nick mine with a saw before they wear out from use. At $160 for a really nice new, eye-spliced rope, it's worth the confidence you'll have in the tree to replace them annually.
I've told this story before but it's worth mentioning again...
I took a 25 year old, heavily weathered, dynamic rock climbing rope (yep, 25 years), cut a six foot section and slippped off the sheath to make a couple of flashy dog collars. The core was two braided pieces, I lost one and used the other one as a chew toy for a 6 month old border collie... one VERY energetic dog.
We trashed that half of a rope core for a few months until you wouldn't know that's what it was. It still seemed really strong so I knotted it and hung on it, even bounced a bit and it never showed any sign of failing... that it held 190# at all was surprising to me.
I'm not saying use ropes for 25 years, or even 2 years, but it's worth knowing that when you retire your lifeline for age (rather than damage), you can be confident it's perfectly safe until the day you stop using it.