OK dude, TDK IS NOT going to break Titanic's record. Period. As I mentioned, women and teenage girls went to see Titanic 4,5 in some case 9-10 times. They aren't going to do that with Heath Ledger.
In addition, Titanic was number for about 15 straight weeks because there was little to no competition during it's run. It came out in December and as we all know January, February, and March are terrible months for movies especially back then.
Also Titanic increased it's box office numbers from week 1 to 2, 4 to 5, 5 to 6, 10 to 11 and those other weeks had very minimal decreases. You don't know what you are talking about so STOP while you're ahead.
Titanic was a very rare breed of movie. TDK is not going to have that deep of a run unless they rerelease it or something like that.
The Dark Knight won't beat Titanic's worldwide numbers, but it's possible it will top its domestic take. The reason is that it's not following conventional box office tracking. Though I doubt it will, it is possible. One reason is the fact that it's the biggest cultural phenomenon there has been since Titanic. And sure, Titanic had females going to see it several times... but I know males who have already gone 3-4 times and plan to go again.
Have you looked at all the releases coming in August and September??? Mummy 3 has the highest chances of making bank and it's likely only going to make around $120M. Tropic Thunder could crack $100M, it could even crack $150M, but chances are slim. That Star Wars cartoon likely won't do a lot, sales will be strong but not on par with other Star Wars. And Pineapple Express probably won't do much more than $80M, if close to that, being a stoner comedy.
So... there's a lot of open business for Dark Knight to reap the benefits of a lame end of summer. Will it do it? Chances are slim... but it will probably crack $500M. But I'd never say never, especially not when this movie has been breaking records like it has.
I remember when media analysts were projecting it to make $75M opening weekend and $105M was one of the biggest projections I saw so... Anything is possible.