Actually, losing the ability overall and losing ability to wield a certain keyblade has no real difference.
There is a huge difference. Losing a certain Keyblade still means you have the ability to wield
A Keyblade. Losing the ability to wield Keyblades means you have no ability. You're not special anymore, you're just a normal person. Xehanort couldn't have opened the door unless he had the ability to wield within him, however, not having memories of the Keyblade, he couldn't actually summon one. (How does one summon something they don't know is there?) This is shown the best in KH2 where, Roxas, in the Data TWTN, having no memories, can't summon the Keyblade (the Keyblade he uses is a fake made by DiZ). It isn't until he under goes his Awakening again does he remember how to summon his actual Keyblade. Xehanort may not be able to summon a Keyblade, but, there's nothing to say he can't wield one (there's actually plenty to say that he can, even in KH2).
So yeah., there's a difference.
if one keyblade rejects someone, what makes you think other keyblades will accept the person at the given time?
It happened to Riku more or less. His original Keyblade went to Sora over him, however, he never lost the ability to wield the Keyblade. Later on, a different Keyblade chose him.
and like those said before, you don't need a keyblade to open the door to the hearts world.
The only things that have been shown to be able to open the doors are Keyblade Wielders. Heartless can devour a world's heart once they find the Keyhole, but even Xehanort said that takes a long time to do (when, opening the door, seems like it can be a rather instantaneous thing). All that's ever been shown to even possibly be able to open the Doors are Keyblade Wielders and, potentially, the Heartless.
So yeah, I would say you need the ability to wield a Keyblade in order to open them. Not necessarily you need to have a Keyblade on you, or whatever, but, it's pretty clear you need to be a wielder, what with the huge importance Ansem put on the fact that Xehanort could open it, and the fact that Riku could open his own.
Nomura isn't going to go "Hurr durr, Xehanort could open it because it was unlocked." This door isn't
just a door. Just like the Keyblade isn't
just a hunk of metal. There are clearly rules to these things.
and if the heartless of the keyblade wielder could use the keyblade, there would be no point in kh1-kh2. kh1 would have no use of sora traveling to worlds just to "lock" the doors.
Why would there be no point? KH1 had Sora locking the Keyholes because it was said that, once locked, the world's heart was no longer reachable. The only Heartless of a Keyblade Wielder who could even possibly potentially wield the Keyblade are the ones who managed to keep a human form (XH, Sora). Both of these people did this, though, through different means. Plus, no one said XH had a Keyblade on him this entire time. If he couldn't remember how to summon it, for example, that means he wouldn't be able to use it. We're stressing that he has the ability to -wield- the Keyblade, not that he -was- wielding the Keyblade through KH1-KH2. And there -is- a difference.
but as for everyone else, they can open any door as long as it's unlock.
When has this been shown? Never. It's not like these doors are just normal doors. There's more to them.
The fact that only a Keyblade Wielder (and the Heartless after searching for a long time) are the ones who can even find the Keyholes/the Doors would imply they are the only ones who can actually open it.
and it would be really stupid for nomura to say "well for the sake of them wielding a keyblade I'm just going to say they chose not to, which led to Xemnas and XH in defeat"
It would be stupid, yes, but he did say he plans to explain that whole situation, which means there is a situation to explain, which means they do have the ability to wield the Keyblade.
Xehanort just forgot about being a Wielder and therefore was unable to utilize his Wielding abilities other than opening the door to DI.
I think you mean RG. Riku was the one who opened the door to DI.
Not saying they wouldn't have helped, but he hardly would've been as desperate about them.
Well, just to play Devil's Advocate or what have you, but in KH2:FM+ Xemnas does say that if Sora is destroyed, their plan could go on without him. Perhaps this was potentially hinting at that?
but really, i don't think keyblades look for anything else other than recommendation and strong heart.
Nomura has said that there are many complex reasons why people get Keyblades outside of having a strong heart and
the Rite of Succession.
So yeah, the Keyblades clearly do look for more than that.
but the way days explanation of dual wielding, i got to believe that Roxas wields the keyblade because Sora isn' technically a nobody.
KH2 paints clearly that Roxas could wield
because he was Sora's Nobody.
losing the ability, and losing a keyblade sounds almost the same thing.
It really isn't though. It's very different.
also i doubt memory loss would mean automatically not being able to wield the keyblade.
How can someone summon something they don't know is there?
Memory Loss doesn't mean not being able to wield the Keyblade, it means not being able to use the one you have.
See why there's a difference between losing the Keyblade and losing the ability to wield a Keyblade?
We've seen in kh2 roxas wielding a keyblade without any know of it
Up until his Awakening (which was him becoming aware of it actually), Roxas was using a fake Keyblade.