Arrowhawk, now I don't know all the books and rules inside and out but I really don't understand why you're reading so hard into this when consensus, here at least, seems to be that they [Druids] are, or should be, immune to all poisons.
I've brought this up with a couple of old D&D buddies from outside my current gaming group who made the 3.0-3.5 transition with me and from the way we all read and understand it, if 'poison' is in the descriptor than the Druid is immune to it (at 9th level and beyond of course). It doesn't specify between 'natural' or 'magical' because it means 'all' - and WotC also didn't say "immune to all poisons except...", so again, all would mean all right?
I see you refer to the 3.0 Druids having only natural poison immunity, well I say that is irrelevant. Should we compare the hitdie of the 3.0 ranger vs. the 3.5 ranger? or the difference in their class abilities? No, we shouldn't because it's pointless. 3.5 made changes that supersede 3.0, so by their decision to drop 'natural' from the Druids poison immunity description and add 'all', unless WotC chimes in on it, we can assume (and luckily my gaming group does) that 'all' indeed means all.
[why the distinction for the Paladin's disease immunity then as you liken this to, unknown - maybe different authors wrote up the different classes and they didn't use the same lingo]
I guess, even no matter what WotC meant in their writing of that Druid ability, that the DM is the final say at the table - it's gotten hard to tell which way you are arguing for anymore; are you playing devil's advocate or are you seriously saying that 'all' poisons doesn't mean 'all' poisons... but if you're the latter, all I can say is I'm glad I don't play at your table
I'm out. No matter what else you say or think, in our group Druids are immune to all poisons once they have that ability and that's all that matters to us - I can't believe this thread is now 5 pages...