Re:
I think you've hit the nail on the head and answered your own question bud! Shimano had so many groupsets bitd that it was only an incremental change from one to the other going in consecutive order.
I would say the jump from Deore LX to Deore DX was much greater than going from 500LX to Deore LX as Deore LX retained a lot of the steel and resin (plastic) features of the Exage lineage, Whereas Deore DX was tricle down (And sometimes just a different finish) from Deore XT, The top groupset at the time and subsequently more race orientated and 'Hardcore' so would have been lighter, stronger and more dependable than lesser groupsets.
Yes there would have been differences, albeit small! and in real world terms I could'nt honestly say how much, but I would guess negligable. I'm sure a marketing man from Shimano could have waxed lyrical but I suspect from a realistic point of view the upgrade would mostly be in the name as even the finish of the two groupsets is so similar as would have been the composition.
One is top of the mid range and the other is bottom of top range, Is one better than the other? Well it must be, It's more expensive and it has Deore in the name like the top group (but actually nothing like it!)...... Gotta love marketing :roll: