Some tobacco manufacturers add certain additives to pipe tobacco in order to keep it more moist longer so as to preserve shelf life. A lot of high quality tobaccos have a lot of naturally occurring moisture that will help it to age properly for 1 year, 5 years, 10 years, 30 years, etc. Once you decide to pop the seal on a tin, it is generally a good idea to dry the tobacco out a bit before smoking because it will provide a drier, cooler smoke which will also give more flavor than moist tobacco. Your assessment, as provided above, is more or less correct in most cases, but everyone prefers different moisture levels in their tobaccos. Experiment and see what works for you.