General :: Relationship Between S2disk And Hibernate?

On a Debian system, there are packages called uswsusp and hibernate. The former contains a program named s2disk, the latter contains a program called hibernate. Superficially, these both do the same thing: the suspend the machine to disk. Usually, this works fine, but since I'm often using Debian testing and there are lots of changes in kernel and other packages (I assume), somethings this breaks. But then, when one of these programs doesn't work, sometimes the other works. Often, hibernate works when s2disk doesn't.annoyingly, however, the "Suspend" or "Hibernate" buttons in the graphical user interfaces (e.g., LXDE, KDE) appear to be wired up to the s2disk program, so when that breaks I have to use hibernate manually.

So, what is the difference between these packages? Interestingly, the hibernate package "recommends" uswsusp, but the package description says that it "smartly puts your computer to sleep ... using one of the various methods available in the kernel". So apparently it can fall back to something else when the s2disk method fails? And if hibernate is more powerful, why wouldn't the GUIs use it instead?