These sorts of comparisons are kind of silly, because there is no way to adequately put all these movies on equal ground (the movie market is radically different today than it was in the 1930s). Even if one could, what exactly are they trying to show? Relative popularity? There are better measures that do not include grosses.

The biggest issue though with comparing a movie that came out a month ago with a movie that came out 80 years ago is that movie has had 80 years of releases and re-releases in which to make that sum. It would be much more fair to compare everything to how it did in the first month of availability (though even then you have problems with judging how widely distributed a movie was initially). Also, the site doesn't make clear if, when taking into account re-releases, they adjust everything at the price level of the original release or if they judge each re-release at the new price level.

In the end, though, any sort of historical comparison is a silly exercise that tells us little.