Spesh don't offer lifetime warranty because they believe in the product. It's a numbers game. How many hardrocks and rockhoppers do you think they shift that only do commutes or very occasional light offroading. They know they won't be replacing these under warranty and the more of those they shift, the more likely they are to not lose out offering the lifetime warranty on the more used bikes, lower volume, higher end bikes.
Orange's are a bit more niche, lower volume, enthusiasts bike (not that proper enthusiasts can't ride a spesh) and they probably can't afford to play the numbers game.
Besides, 12 years of Oranges and I've never broken one…
(Of course if I do break my Five it'll be covered new for old on accidental damage to goods away from home)