Can you cite some text to support this assertion? And for a lot of skills this interpretation doesn't work, because what is "normal circumstances" for picking pockets? And how would that interpretation apply to hearing noise or reading a magical scroll?
I'm not sure what to make of your assertion being that originally they automatically succeeded at things, given I've never read that anywhere, and the only place automatic success shows up is in a note in the 1e AD&D DMG about thieves can set traps automatically with enough time if they have appropriate tools for making a trap because in this one circumstance only they are allowed to reroll failed results.
Where did the groups you are talking about get the idea that automatic successes were intended?
When it was originally written, that's how it was. The original write up didn't even have percentile chances or other items, that was (I believe) added by Gygax later.
That's also how many played it back then. There wasn't something that said...oh...you have to roll under a percentage to suceed at this skill...etc, that I recall.
For picking a pocket...you just picked the pocket. Unless there was some reason the other person would be able to notice, you just did it. If you tried to hear noise, it just worked.
This was with OD&D...AD&D 1e it was still there, in theory, but that's where you see the implication on it in the rulebooks really change the approach to needing to roll for it everytime.
Previously, part of why it was done differently is because the thief was not an original class. Originally, anyone could try pick a pocket or move quietly or to hide behind something or to listen at a door....etc. How this was adjudicated changed from group to group.
When the thief came about it did not automatically change how people were playing. It didn't mean that suddenly your Fighting Man could never attempt to pick someone's pocket again, it just meant that the Thief was able to be trained in it.
I saw...basically two approaches at that point. The most common is that unless it was contested, the thief just suceeded. They didn't have to do an ability check or roll like everyone else.
Another method (and this continued a little bit into AD&D, but the tournament scene sort of killed it) was that everyone could attempt to move quietly (or other skills similar to what a thief could do, but inferior to them), but only the thief could move silently. Thus, even if the thief failed their roll, they still got the ability check to succeed that everyone else got.