I'm pretty sure I wrote that Q&A answer in 2005 (I was head of the Q&A process). Those were our (my) interpretations and the IRS agreed with them. That's not so say someone else at some other time at some other part of the IRS would have a different opinion, but I stand by those answers. So, a couple of things....
If you are "interpreting" it and trying to use "precedent", I think you are in error. Either an employment relationship is continuing on 12/31 or it is not. If someone is terminated as of 12/30, they are not employed on the last day of the year; period. We have this discussion with clients all the time and it is the client's call to determine what the termination date is. I should point out there are other issues at play: worker's compensation; unemployment benefits, health & welfare benefits, etc.
This is NOT a facts and circumstances issue; it is a factual issue and the employer makes the determination.
I disagree with my good and old friend Tom on the issue of the strict Christian. Whether he ever worked on Sunday or not, if Sunday is the last day of the year and he QUIT on Saturday, he is not employer on the last day of the year. If he turns in his resignation and says he quits as of 12/31 and the employer doesn't countermand that, then he IS employed on the last day of the year. This is ALWAYS an employer determination, and the question to ask is always: "is there still an employment relationship on 12/31 or has it ended prior to 12/31". Simple question (but I acknowledge not always a simple answer because many clients don't think about it when someone quits on 12/30).
On the other hand, my wife and I got MARRIED on 12/30 (many MANY years ago), so we know how important the difference is between the last day of the year and NOT the last day of the year! :-)