Watchtower appears stagnant because -- well -- it is stagnant. Put yourself in the shoes of the GB. In order to be creative, their writer zombies must say things differently. When they do that, they know what they say is under the microscope of an army of critics -- enemies and apostates as they like to call them.
Critics, since the early 90s have had the WT Library CD, which the GB probably regrets. This has become a two-edged sword, helping the more serious members of their flock research certain teachings as they prepare talks and arguments. However, the CD has hugely reinforced the army of critics as they can now quote verbatim snippets of now embarrassing and undeniable statements they've made in the past. This will never stop since the cow is now out of the barn.
Change something that's been written before (impossible to do) and critics will rightly view that as a contradiction. No sooner than critics hear it, critics will publish it, not only here but in the growing multitude of excellent Internet sites.
Change something, and they then must lean on their New Light alibi -- and that worn out catchphrase is not ringing true any longer with members who have a decent amount of gray matter.
Stagnant? YES SIREE, BOB! You can also call it paralysis.
Len