A lot of it has to do with the satisfaction of your gaming group with the edition you started with. If you were VERY satisfied with it, and it met your needs 99% of the time, chances are you have no need to change. Everything new seems unnecessary.
On the other hand, we have groups who ran into difficulties with the previous rules-set, or were never exposed to it in the first place. Their impressions of these difficulties, and how they handled them, influenced their view of that edition.
The reason many gamers (I hazard to say most of the D&D gaming community) switched to 3E upon its release was because they perceived that 3E solved many problems they had with previous editions of the game. Whether it was a series of minor irritiations, or whole subsystems (such as multiclassing), they perceived greater value in the newer system, and switched as such.
Other players did not see the value in the codifying and standardization of all of the rules, or see the value in the different approaches to things such as saving throws, multiclassing, character classes and unified XP tables, standardizing hit point gains from 1st to 20th level, etc. These things changed the "feel" of D&D, and as such hurt its viability to them.
For instance, with the layered multiclassing system, feats, and the skill system, the traditional fantasy archetypes of D&D (Fighter, Mage, Cleric, Thief) were weakened in favor of introducing more heterogeneity in PC's. A character takes far more to be described mechanically now than before. All these things detract for a fan of 1E or 2E from the beauty of simplicity in the AD&D system. (Anyone from the Dragonsfoot forums who posts here feel free to correct me if I have these basic ideas wrong.)
A fan of 3E, however, will look at these same mechanics, and prefer the shades of gradation present in characters available now, and the unified rules on doing this.
In 1E, you make a basic character, and work with your DM if you want something unique or "cool" in his quiver of powers. The DM adjusts your abilities or XP chart accordingly, and goes on. Far less rules needed, but your effectiveness versus the other players' characters is mainly determined by the experience of the DM.
In 3E, the only thing you need to do is pick the appropriate cool ability from the Player's handbook plus supplements allowed, then show the final product to the DM, who approves or denies it. Among the core books at least, the consistency of the feats, skills, and class abilities are such that 99% of all character options are well balanced, and the DM has to do less work on ensuring that his players' PC's are all within the same range of relative power. The goal of 3E was to constrain the min/maxer's top end of power to a certain limit, and let the DM concentrate on his campaign.
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In practice, many people have found many different results. One poster, Flexor the Mighty (Hi, Flex!) has found that the new rules actually hamper his productivity with degrees of complexity. Having been used to the simpler set of combat rules in 1E, he was used to spicing up his action scenes with drama and creative interpretation of the results of dice rolls and player actions. Feats and skills, rather that freeing him, have complicated the picture badly for him. (Flex, if I misunderstand your position on this, please sound off.)
In the end, the same rules apply. (1) Your experience with the system determines your comfort with it. (2) If the existing system has worked well in the past, there is little incentive to change. People often find it bizarre to hear someone in the computer technology industry to say this, but "newer" doesn't always mean "better."
In my case and 3E, however, it does.
