Lastly, here's a really good argument to protect, and you can see it with all kinds of marginals, not just palms. I have often had mulched plants severely damaged or 100% killed to the top of the mulchline. But, pull off an inch or two of the mulch in spring, and the rest of the plant is alive and well. If mulch works wonders (and it does), then why not other forms of protection?
Through a lot of trial and error, I've come to the conclusion that ventilation is very important. There needs to be air exchange in any protection scheme in Zone 7a or warmer. And you have to have some kind of system for making sure your protection scheme does not overheat and literally toast the plant.
Of all my palms this year that I protected, the only one with a negative result was the Hatteras Minor. And, maybe not a random coincidence, it was the first time I tried a different protection method: Burlap wrap with a clear plastic trashcan liner bag over the whole thing during precipitation and severe cold events. It may be that I left the bag on too often for too many days. This is how you learn.
One final argument for protection: Since 2007, I have had two palm fatalities. A Brazoria Sabal and a Palmetto. The former had no protection but mulch and died after a winter low of 7F above zero. What I did for the latter was to pop a mini greenhouse on it for a couple of winters. Well, after the ultra mild winter of 2012, the palm showed a lot of damage in the spring, but was still living. I couldn't get over it. How could it be? So, the next winter, no more greenhouse. That winter killed the Palmetto. Who knows? Maybe it was just a lemon of a palmetto. After all, I do have one that is a 10 year survivor!
Protecting in moderate winter zones like 7a, where -10F temperatures are a once-in-a-lifetime occurrence, and -5F nearly as rare, is a question of BALANCE. One can easily go overboard with protection schemes. My experience tells me these are written in stone:
1. Mulch is king. Every year. On every marginal.
2. Provide a winter windbreak for any exposed marginals.
3. Provide winter shade for those plants sensitive to the combination of cold and direct sun.
Eight times out of ten, just doing those modest things is enough.