I'm no expert on this, but I just did a quick Google search and found this:
http://www.nwa.com/plan/guide08.html
Since this seems to be the policy of Northwest, I don't see how it could be a federal rule. But like I said, I'm no expert and perhaps this page is out of date. I also looked for "positive passenger bag match" and came up with a page on the TSA's site:
http://www.tsa.gov/join/business/areas-of-interest.shtm
It talks about various technologies and procedures the TSA uses but I certainly don't see these as being written in stone (ie, federal law).
I also don't see the "obvious security concerns". All it theoretically does is stop non-suicidal terrorists. I think we can all agree that there are plenty of suicidal terrorists. And even then, what is to stop the person from checking the luggage and then simply not boarding the plane? I don't know this for sure, but I highly doubt they'll take the time to get that person's luggage back off the plane once it's already been loaded.
If you have any specific information as to where it is a federal law I'd love to see it. I'd also like to know what other security concerns to Delta that voluntary separation imposes.
I've been personally burned by this before (at MCO, no less). I missed the 45 minute window, and since it was my first time doing that, wasted 15 minutes trying to figure out what to do next (thus missing the 30 minute check-in window). Thankfully I had already checked in online and was able to have the counter agent reprint my boarding passes and check the bag at the gate. I have Clear so that helped me speed through security.
Now I'm a little smarter and always travel ready to take my bag through security if need be. I also always check in online first so that if I miss the 30 minute check-in window I'm not screwed. I also like to fly out of DAB since the bag check-in time is 30 minutes, and I've even had a counter agent check my bag after that time just because she was being nice (and it's like a 100 yard walk from the counter to the belly of the plane).
PS. First post. Discovered FlyerTalk last month and I love it. I've learned so much.