1) The wall is either built w/a header in it (when the 'pocket' is in a load-bearing wall), or 2) a cripple is built when the wall is NOT a load bearing wall. In BOTH cases, neither the pocket nor its framing is 'carrying' any load. In #1, the header is carrying the load and in #2 there is no load; just framing ALL around the door (except on the bottom since the bottom plate needs to be removed. If it's not removed, the pocket will sit up 1-1/2" off of the floor.)
3) If you turned studs sideways, and you did the math, you'd realize that 2 studs turned sideways totals up to 3". A 2" x 4" is 1-1/2" x 3-1/2", thus, 2 studs turned sideways = 3". This means that the door can only be 1/2" thick. And you can be SURE that is w/o any tolerance on the sides. In other words, it's a TIGHT fit.
Now, you're (probably) going to say (or thinking) that you only need 1 stud turned sideways. No, not good. This means that you're supporting what's above the stud is only being supported on one SIDE (or 'end') of the header. Well, a header is usually 2, 2 x 'somethings', up there. What about the 2nd 2 by ? ??? DEFINITELY not a good situation to be in! Even if the header was an I-beam, a 2 by would still need to be perpendicular to the beam to be of any use.
RE: Metal studs - The pocket door 'kit' doesn't use metal studs. I am being more 'particular' here but it's simply the pocket framing that's metal. Again, they're not called studs. First, you 'frame' the wall to 'house' the pocket kit. Then you install the pocket kit (or frame) into the stud framing. The pocket kit is ATTACHED to the 2 x 4 framing. I guess to me, studs implies more vs. pocket framing.
Please, don't think that the pocket is what's 'holding up' your wall (in either a load or non-load bearing situation.) It's not. It's the wall's framing (including the header if applicable) that's holding up the wall. The pocket is 'just there'. It's just housing a sliding door, and nothing else. I hope this alleviates any concerns and clarifies the entire construction situation. (I've said a lot so it's possible I did nothing but confuse you all ...)
My best to ya and hope this helps.
Jay J -Moderator
PS: Visit the Pocket Door Links I provided in my initial How To follow-up to Melissa.