Playing psychologist might be fun, and you're probably right that people who lie in polls will do it in the most absurd way possible, but I don't think it's fair to conclude that this tendency accounts for the numbers we see here.

The "over 100" category in this poll is actually a very broad group. It includes not only those people who sent slightly over 100 letters, but also all others above that. Consider the people are in jobs where they send out hundreds, thousands, or perhaps even tens of thousands of letters per year. First, this group is less affected by the decline in personal letter writing, and second, every single one of these people is pigeon-holed into the same category of "over 100". It's no wonder this group is slightly larger.

GPG is a name chosen to describe the free version.
This sentence is neither informative nor funny.

No, GnuPG is not the same as PGP. GnuPG was in fact developed to replace PGP, both because PGP is covered by a non-commercial use only license, and (probably) because it by default incorporates the patented IDEA algorithm. Yes, PGP Freeware and GPG are both free and interoperable, but they are not the same thing.