In the end, they decide based on whatever they decide. But their general rule says:
"For a work to be eligible for inclusion in the database it must be of general public interest and should be available to the public or have been available in the past. "
"General public interest" can mean that the project involves a name or company that verifiably exists and has a track record. So yes, there's a certain level of favoritism, only because if Paramount says they're shooting a movie, IMDB has good reason to believe it, even before it comes out. Or if there are any reputable third-party sources that can show why the project-to-be is of interest - a magazine article or something at the very least.
Without something like the above, there's no reason for IMDB to believe the project exists at all until it's assembled and viewable by an audience. Once you can prove THAT happened, then a listing will be much more likely to be approved.
But you can see why IMDB works this way - the number of vapor-ware project submissions they receive, that then never really amount to anything, must be staggering.
The IMDB Eligibility FAQ
