Is there ever a reason for Protoss to not build Zealots, Archons, HT, Stalkers against Terran?
You don't understand what I'm saying. If you play Mech I'm not going HT Storm, and if you play Bio I'm not going to go mass Gateway.
I disagree. If the terran goes mech, the protoss would and should go immortal, because it is probably the most cost-efficient thing to do in the entire game of SCII. This means that the terran will need to supplement his army with something that will kill immortal which would either have to be marines or banshees. In either case, HT/Archon would still be very good for storm/feedback and Archon just beats Terran units in general.
Zealots and stalkers are the bread and butter of Protoss. I can't imagine a single scenario in TvP where you wouldn't have those 4 units, just because of how effective they are as a general composition.
Edit: I suppose you could try to go ghost instead of banshee or marine, but again feedback is pretty good here and archons would still be good against them. I still think zealot/stalker/HT/Archon is a good composition to most anything terran will realistically do.