There hasnt been a new movie in over 20 years for starters and Indiana Jones is more adult oriented. I think more parents probably figure Star Wars is going to be at least a bit lighter and perhaps a bit easier to understand. Plus look at how kids took to Pirates and Spiderman. Its the influence of it being in theatres.
When I was a kid I LOVED Star Wars. And now I cannot help but hate it. It was the prequels, they killed the entire concept for me. I had the vintage figures from my dad, Potf2 figures the day they came out, posters, I was Darth Vader for halloween and had lightsaber battles, played the CCG, read the books, comics, i even use to be able to recite the scrolling prologues from memory when i was like 10. So its not like I wasnt a real fan, but the moment I stepped out of that episode 1 showing it all died, right there in the lobby. I returned the Darth Maul figure i had bought out front of the theatre, sold all of the cards, books etc. I felt like all my life George Lucas had worked his ass off to prove to me that Santa was real and then in one moment, he personally shot Santa in the face. The fact of it is, no matter how much you tell yourself that there two seperate trilogies, it just isn't true. Its all one story. If they went back and made a prequel to the Godfather, and lets say to be more 2008 culture friendly it turns out Vito Corleone once fooled around with a guy(I have nothing against sexual orientation people should do what makes them happy, but alot of people would not be ok w/ this.) The point is you wouldnt still be able to watch the Godfather w/o thinking about that.
Indiana Jones however, has maintaned his same level of popularity, not really exploding to a level of well known culture like Star Wars or Batman. Not to say he is unknown either. What im getting at tho, is he hasnt had to change to appease a new genre like Batman tryed to do w/ Forever and B&R. (Thank God for Chris Nolan re-inventing the franchise.) So with Indy 4 your going to see alot of young kids getting into it, which will lead to more products and Indy related material. And generations of Indy fans to come. I assure you all right now however if a Temple flies off into the sunset twoards Jupiter in the end of this flick, I will personaly dress up like an ewok, infiltrate skywalker ranch, and punch Mr. L square in the mouth.