I've seen very little of his work and I noticed that (one or two episodes of Buffy is about it for my prior Whedon-watching.) It definitely was deliberately written to make newbies realize that...the first time the characters are in real danger is right after Wash's death. At which point I'm thinking, "They may not all come out alive..." As opposed to every other sci-fi movie, where the only dying characters seem to be either tangential or the death is really frickin' obvious (Trinity in Matrix Rev., The Terminator in T2, etc.)

And that's why I'm now a convert :)