This isn't necessarily true. All schools break admission decisions up differently...some schools have one person that verifies prerequisites, and then the applications get split up alphabetically and reviewed by different profs, and then to another committee, etc. This is a long process for each individual application (except the ones that are a clear no, which I'm sure get thrown out right away and probably notified).
The closer you submitted your application to the deadline, the longer it'll take. When I spoke to NU admissions last year about applying this year, they told me to get it in early because some of those who sent in the application on the deadline didn't even get looked at - PTCAS took a long time to verify prereqs and all that info so by the time the apps got to NU they had already made most of their offers.
As they get more applications, it takes longer for them to get to them all. My friend and I both got into NU - my app was mailed 2 weeks before his, but he found out he got in a month after I did. Those two weeks played a huge role in the delay for him to get an offer phone call.
Don't freak out yet - some schools deadlines haven't even passed yet, and some of them may not look at applications at all until that date. I know someone who is married to someone on the admissions board at UIC, and even though their deadline was Oct. 15, he said they don't even look at an application until mid-December (they make sure they get all of the apps before they start looking at any of them). I think they still look at them in a chronological order, though....not sure.
If you were an absolute "No", they probably would have told you by now - no use in stringing people along that they know they won't let in...it could be that they either haven't looked at your application yet because they're so piled up, or maybe you're in a "to be interviewed" pile and they have to figure out how many interview dates they need before they start offering interviews, or maybe you're in an on-the-fence pile and they have to review it again. It could be any one of these, so no need to freak out yet.
I know someone who didn't find out he got into PT school until end of April/beginning of May, just because of the number of applications they received. Don't start freaking out yet! There's still plenty of time 🙂