*note for some reason I was on page 95 and thought I was at the end of the thread when I wrote the below post and thought it was relevant to the current conversation, it's now actually slightly off buuuut sorry lol*
I can't really explain WHY exactly, but the role of Indiana Jones is one of the few I consider to only be playable by one actor. I think Harrison just plays the part so perfectly that in most fans minds they really see the two as one. If I never saw how Harrison played him, and only read the lines as they were written in the script... I don't know if I would have found the character as interesting. If I had see Raiders, but with a different lead, I don't know if the actor would have poured in all the right ingredients. Harrison being who he is, Harrison Ford, instills some kind of charisma and charm that only he can add. Anyone attempting to actually do the same would never quite work as well and I think I'd have a tough time accepting the character.
I mean, even down to the look Harrison is perfect. I don't know about anyone else, but every time I see someone dressed up as Indiana Jones I always feel like they don't REALLY look the part. Think about all the different actors out there, who would really look as good in the fedora and jacket as Ford? There's just something about the guy. Ever notice how hard it is for toy makers to get Harrison's face just right? And often it makes the figure of Indiana Jones seem off? That's how important and synonymous Ford has become to the role.
I don't think anyone else should play Indy... because my interest in the continuation of the character on film is always tied to him as Harrison Ford. When I read IJ novels I always picture it as Ford in my mind. It's like Ford IS Indiana Jones. And in some ways that's completely true.
This is of course, my own view on it. I'm sure not everybody is as wacko for Ford as me. I wouldn't be against a different actor playing him in the distant future, but for now I want to see what Ford's Indy is up to now in the next installment.
I also think, it will be a lot easier for audiences to accept an older Indy after KOTCS having come out. I don't really think Ford's age really hurt the movie or anything. The things that didn't work were not the fault of Indy's advanced age, which is what most people were expecting.