I never knew their recommendations until you mentioned them but it's possible they could be right. It's also possible they are overshooting for the purpose of playing it safe. Can't really blame them if that is the case.
One thing the think about is the thickness, a 5# cut that is only 1.25" thick is going to have a totally different heating time than a 5# cut that is 4-5" diameter. The 1.25" is a much shorter time.
The other is a margin of error, USDA says that cured, pre-cooked ham is ready at 120F internal. I feel that 4% at 125F is fine, especially for something that is cured with nitrates and salt, then cooked and finally vacuum bagged in a controlled environment. 140F is very safe, but I think it might dry it out. I've reheated cured, smoked pork chops with the SV before and I found that the lower the temp I use, the better. 145F killed them. Of course chops are a less moist cut than a ham (hind leg) but I still think that the lower the better in this case. After all, since it's already cooked, all you are really looking to do is heat it up to where it is appetizing to eat.