The same could apply to the Aerith appearance too, but he doesn't ask if it's her does he?
Heeeey.....I just had an idea. Aerith didn't appear to Cloud until he approached the Forgotten Capital. That's where she died, maybe she chose to appear to him then because her power is stronger there somehow or something.
When Zack appears during the fight with Sephiroth Cloud didn't ask if it was him. He just said his name out of surprise, maybe even relief. But he wasn't asking, "Yo Zack is that you?" lol
Also the times and instances of Aerith's appearances is a topic that I have discussed at long length with other peeps before. You've hit the tip of the iceberg with that observation, Drake. Want me to explain my theories on the rest?
Well I'm going to whether you want me to or not.
1.) There is a hint of her in the church after Cloud and Tifa both pass out. Only a hint for now, mind you. She's still being blocked by Sephy. But she can come out a little bit because it's the church, which has a tie to the Lifestream and is also her own little sacred space.
2.) She appears near the forgotten city. Where she died, yes, but also sacred ground for the Cetra. This was the only place in which one could go to summon Holy. It would be safe to assume that this place holds much power as well as a deep connection with the Lifestream. Creepy cell phone scene is included in this.
3.) She appears inside Bahamut's energy ball. Summon monsters are called forth by materia using the memories and energy of the Lifestream. Yet again a connection that we've seen once before, and Aerith appears in within it? Hmm...interesting.
4.) She speaks to Cloud after Kadaj messes up her church when the water breaks out. Lifestream mixed with water and Aerith's next appearance? I do say...
5.) The purifying rain has been released, but is still blocked from falling by Sephiroth's will. Aerith is seen praying for Cloud's victory, but there isn't really much she can do here it seems.
6.) Sephiroth is defeated, and the rain now falls freely. Aerith comes for Kadaj, and even makes her presence known to Tifa on the airship. Aerith's presence is now able to go wherever the rain falls.
7.) Aerith heals Clouds wounds, but this time is in some weird life/death limbo. Now said to be Cloud's promised land in the Ultimanias. More Lifestream? I think so.
8.) I'm assuming that since her water is still everywhere and it's so soon this is how Aerith was able to make the phones ring. But maybe she made the call from the church? lol
9.) Last appearance in the church, which has been covered before. We see her going off for good this time to presumably join with the Lifestream finally.
Either way I think that's it. The phone part is a new addition to my theories and I haven't given much thought to Zack yet. I came up with this a while ago now. lol
I would assume, though, that due to his absorption of parts of his memories and personality/mannerisms that Cloud and Zack may have an indestructible connection. This could, however, also be due to the water being released in the church. The effects are still being held back by Sephiroth, but perhaps Zack wasn't. Maybe only Aerith with her connection to the planet was held back.
And those are my theories.
Just theories mind you.
But yeah it's interesting how all of Aerith's appearances seem to be only when there is Lifestream nearby.