Wirelessly posted (BlackBerry8830/4.2.2 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/105)

I assume that you mean seat assignments are gate restricted, not check-in, right?

If so it is usually because too many seats are assigned and they need to keep them available to handle swaps and whatnot for families, etc. That being said, I've only ever seen that situation before OLCI opens. Usually at OLCI more seats are opened up to accommodate folks checking in.