I don't think the recession has anything to do with CBP being tougher on TN-1 than USCIS, it's more to do with CBP coming into existence basically as far as I can see and hiring tons of new staff. A lot of TN-1s issued in the past were not that thoroughly checked, so when USCIS receives an application to extend it then they don't seem to check too closely because the person isn't there.
If you're a POE obviously they can ask you the question and look it up in the manual and check more closely.
I think initial applications are best done at a POE because you're there to answer their questions (plus it's not possible to do it any other way in most cases). Extensions I think boil down to what category you're in and how close to a POE you are. Because it can be cheaper, quicker and easier to go to a POE as it saves filling in I-129 and the fee is only $56.
Case in point. Obviously he'd been filing inside the US and it wasn't checked too closely. Years later he had to go to a POE and was denied.
Steve.