Look at them, and ask why we don’t do “it” “that way” any more. Did it just not work, or did they come up with a better method. Or, did someone just forget. Maybe there were camps on one side or the other, and one side won out when the next version of the game came out. For instance, it could be that the thief lost out to the niche protection of the magic-user, who has spells to deal with magic traps/locks.Not to pick on Jeff, but that’s completely backwards thinking. Not only is it based on the false belief in Objectively Good Design, but we know in fact that people were playing D&D before the first three books were even published. It’s not “alpha” – that may have been Arneson’s campaign before he teamed up with Gary. It’s not even “beta”; that would appear to be something like the ”Beyond This Point Be Dragons” document. By the time of the LBBs, there were several people running OD&D in a form we would recognize, although each had their house rules because making your own house rules was still officially part of the game. We also know that Greyhawk is not a later clarification of the LBBs, but Gary’s house rules, which were already in use before the LBBs were published, but were left out because there was just too much stuff to put in the planned three booklets.
And, in any case, AD&D is certainly not the beta version of OD&D. We know why AD&D exists: Gygax and Arneson got into a legal dispute, and AD&D was designed partly to create a game Arneson had no claim to, and partly to act as official tournament rules, for people who wanted a standardized set of rules. It’s not a replacement of OD&D, because OD&D became what’s known as the “classic” line: Holmes, B/X, and BECMI. If a descendant of OD&D was being sold alongside AD&D 2e, we can’t really call AD&D a “beta” version of OD&D, can we?
But leaving that aside, let’s look at that central question: why were certain things dropped? The most common reason is, indeed, that someone forgot why the rule was there. D&D was created by taking stuff that already existed, adapting it to fit some new idea that sounded like fun, and if it turned out to be fun, it was kept. Some things are there specifically to support certain ideas; for example, XP for gold being more than XP for combat is there so that there a greater incentive to avoid fights where possible, and XP requirements that pretty much double every level are there to make it easy for new, low-level characters to catch up with existing, higher-level characters. When people forget or never knew why those things were the way they were, they changed it to make it more “logical” – and created problems, which they tried to fix, creating more problems, and so on.
The thief Open Locks ability is a good example. Gygax, as it turns out, didn’t forget that it applies to magical as well as normal locks. I checked the PHB to be sure, and there it was, on page 27:
Opening locks includes figuring out how to open sliding puzzle locks and foiling magical closures. It is done by picking with tools and by cleverness, plus knowledge and study of such items.I don’t have the 2nd edition PHB anymore, so I can’t check to see if it is in there. But definitely, every discussion I’ve seen about thief abilities acts like this is mundane lockpicking, and that Hide in Shadows is the same thing as mundane hiding, and Move Silently is the same as being quiet, even though the PHB makes it clear these are supernormal abilities.
And what do we see in discussions of thief abilities? Complaints that the thief is underpowered. Why? Because people forgot what the thief was really supposed to be able to do.
And yes, as Jeff suggested, part of the reason people forgot that the thief was supposed to be supernormal was because “thief” is not just a class name, but also a profession. I’ve complained about this, myself, although I think the Cleric was the first class with a bad name.