Actually at launch, they do, kinda. Basically when a new expansion launch, the main raid isn't available right away. 2weeks after launch the normal version is available(LFR) and 2weeks after that, savage is available. The whole tier is available at once though, and they only do that for new expansion, to let people take their time enjoying the story, leveling alts, getting crafting/gathering up, getting used to new rotations and this kind of stuff. It's the only thing though, either a raid is released or it isn't, there's no gating encounters behind timers. Granted XIV raids are only 4 fights per tier(but there's 3 tiers every expansion, plus 1-2 ultimates, plus the extremes which are easy encounters but could count as the simpler raid fights, plus the past 2 expansions the weird 48man stuff).
I'd say personally I wouldn't mind too much though depending on how it's done. If they're drip feeding encounters after the timegate, that'd suck, but if they're like withholding say half the raid for later I think it'd be ok if "later" means a few weeks and the half that's available is meaty enough. No idea how they're going about it though.