I thought this was more of a trophy room. These Jedi were on display. And, being on display like this, really drives it home to Obi-Wan just how bad things really are. It's one thing to kill your enemies, but, to turn them into hunting trophies is horrific. And, wouldn't this be something of a trophy room for Vader? This is how far Vader has fallen (as if we needed more - but, this is all pre-Episode IV so, Obi-Wan hasn't actually seen just how bad Vader really is yet) and presumably goes a long way to convincing Obi-Wan to not tell Luke who his father really is. I mean, there's a difference between, "Your father is the right hand man to the Emperor, he's really bad" and "Your father is a psychopath, child murderer who keeps trophies of his kills".