They're reactive as roleplaying games, not as "worlds" that are simulated. Everything is scripted and even then, we're talking about first order consequences for your actions, not second order or anything specially sophisticated. That is, people will react to you if you're a child killer or slaver, or if you kill a crime boss, but your actions won't generate their own unforeseen consequences and so on. You quickly run into limits when you try to accomplish that in a scripted game, hence Iron Tower's famous gating of content in chapters with points of no return. If you want deep, unscripted reactivity, you need complex simulation of the Dwarf Fortress variety.
Fallout is still a gold standard for RPGs because of its fortunate mix of RPG elements. You have a large variety of roleplaying options, you make meaningful choices, the world building is stellar, it has a timeless aesthetic, and it avoids many of the pitfalls of other games. For most of its component parts you'll find other games that give you more options, but you won't get the complete package the same way you do with Fallout. It'll probably be a long time until one can say Fallout is obsolete, if that ever happens.
The question in title however asks for interactive "worlds". I also disagree that those two (true reactivity through simulation and "roleplaying") things are separate. Good simulation and world reactivity would be great for CRPG purposes in certain sub-genres. It simply is too hard to achieve, as you said, but it isn't unwanted.
I agree that to get a world truly reactive to player action you'd have to simulate it not just script it. The latter becomes more complex exponentially as the amount of elements you can interact with and can interact with each other increases. However i believe that even scripted reactivity still has untapped potential. At least potentially, lol. It just requires a lot of work, work that isn't rewarding financially. VD's studio is one of the few that really tried to advance this a bit - with mixed results. Scripting combined with limited resources means limited success no matter how enthusiastic one is to the idea of reactivity. So what's left is either a different approach or an AAA game (="unlimited" resources) - the latter will never happen. Or just games like we have now ("fake C&C games" i call them) but slightly better, at best.
My biggest hope is, in the future, the AI. However it might be a false hope and it simply can't be done that way. Or it can but no one will ever do it. That or some super-autists like the Dwarf Fortress'' guy. People who can work on a single game for decades.
However one thing that should be said is that both methods, scripting and simulation could be combined to good effect. Then again maybe not.
As to Fallout 1, it is still very good as a game and not obsolete. The question however was about a golden standard not just as a CRPG in general but as a CRPG with reactive world specifically as per the thread's title. In that regard there are better choices, Fallout's world is very static. Even Arcanum, possibly a worse game* in general, has more reactive world even in not by much. Then AoD. People mentioned F:NV, never played this one. What abut Colony Ship? Several more games were mentioned in this thread but i never played them.
*JarlFrank, please don't kill me.