Metastatic dz: I am very surprised that your app is on hold. It doesnt matter what school you come from in the US, a step 1 of 250 with positive LORs etc etc should automatically qualify for an interview at NYU and most places for that matter.
I think what is going on here is a phenomenon that is a by-product of the electronic application system. It is so easy to apply that the same people have flooded all of the more desirable programs with applications.
Now the people who receive 20 invites and their list reads: hopkins, mgh, cornell, columbia, nyu, mt sinai, mayo, duke, BIDMC, BW, yale, ucla, ucsf, wash of st louis/barnes-jewish, etc etc will most certainly not be able to attend 20+ interviews. Those people will start canceling by the end of november. At that time, the program directors will probably review the apps which they are referring to as "on hold" and perhaps offer some invites to fill their annual quota of interviewees and insure that the program directors' rank list is long enough that the program does not go unfilled.
Basically, the programs do not want to reject too many people too soon because once they send the rejection, they cant exactly go back and offer the invite. It sucks because the programs are hedging their bets and it keeps everyone waiting, but I guess it is also good because if you do get the interview, that means you have a chance of making it to the program director's rank list and did not just waste your time and money traveling to some place that does not want you anyway.
If I have not heard from a program by now, I am personally assuming that I am not one of the "favored" applicants to that program even if an invite does eventually roll by. Other people might have different opinions.