Good post Neozobian! I think you accurately described the issue for a lot of people. Indy the character as embodied by Ford was a hero to many in the 80's, and to see him now at the age Connery was playing the "old man" professor in LC, is a bit hard to swallow. A lot of people want to remember their heroes, icons, etc. in a flattering light. No one likes to think of the 1970's, fat, drug addicted, fried peanut butter, butter, and banana sandwich eating Elvis. They like to think of the young, good looking, Heartbreak Hotel Elvis. The same goes for so many actors, musicians, etc.. To see your heroes as older is to realize you're older now as well.
Granted Ford is incredibly fit and still looks good at 65, but he's still 65! He's an older man now nearing 70. He may not play it in KotCS, but it will still be on peoples' minds when they see him on screen again. Continually it will be going through the audiences' heads, wow Ford is not a young guy anymore. Gone is the younger Ford of Star Wars, Blade Runner, Raiders, Temple, etc.. This doesn't mean an older Ford playing Indy won't be entertaining, nostalgic, and fun, but it will be different.