The people I know with Rancho include those that needed to replace them...so, that is how long they lasted....the warrenty coverage is another matter, unrelated to how long they actually last.
So - The warranty on a Hyundai is longer than the warranty on a Mercedes...I guess that means Hyundai's last longer than Mercedes?
I'm not bashing Rancho, its just the Bilsteins last longer...I know people who like both, just more who like the Bils...And I liked the Bils better on the Jeep before I liked them better on the X.
And, as to the actual coverage...from what I've seen, "under normal operating conditions" does not include driving off road, at least for people trying to get new shocks, like in my club, etc.
So - the Bilstein recommendations on this thread are pretty much the collective experience of this group....including those that prefer the Ranchos.

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- TJ
2001 Xterra '03 VG33, SE 5 spd, 305/70/16's, Revolvers, UBSkidderz, Doubled AAL's, 3"SL/2"BL, winch/bumpers, skids, sliders, OBA, Snorkel, pine stripes....
Friends don't let friends drive stock.
http://www.gifsoup.com/view/501230/tj-tackling-crawlers-ridge-o.gif