It also means that there's a fixed target that can get an extended amount of testing in the field, and when fixes for that version come out you know you're getting issue X fixed but no other change in behavior. Less chance of incidental breakage.
Um, no, I have not seen anything that would be the case for upstream Linux. Sure, downstream distributors like Red Hat might be able to give such guarentees, but they do not generally use upstream LTS releases directly.