FireLance said:
As for the rest, I think they are more "things that the rules or flavor are silent on or are not explained well enough" than "errors" or "mistakes" per se.
Why does an attack roll or saving throw always fail on a natural 1? The rules say so. It's the flip side of attack rolls and saving throws always succeeding on a natural 20.
In 3e, saving throws auto-failing on a 1 was not in the rules. Depending on who you talk to, it was deliberately omitted. Skip Williams, however, decreed in the FAQ that a natural 1 auto-failed on a saving throw, based on pretty much nothing but that being the way he liked it. This became even more irritating when the errata came out for 3e, without any mention of this rule change, leading to much confusion.
(In 3.5e, however, for better or worse, it is clear in the rules that a natural 1 is an auto-fail on a saving throw.)
Personally, 1s auto-failing on saving throws is a bad thing. Randomness disfavors the PCs--they will be in many more encounters than any NPC and are more likely to have saving throws high enough that whether or not a natural 1 is an auto-fail or treated normally will matter.
The comparison to attack rolls is inapt. A single attack is generally not going to kill you (or if it can, it's unlikely the attacker would miss with a roll of 20, with or without auto-success); however, there exist a large number of spells that will immediately kill a PC. Given the adventuring career of PCs, they will more than likely be hit with more than 20 of them. Statistically, they will roll a natural 1 to at least one such spell.
(We'll also leave aside the other issues. For example, while the group of 20 1st level fighters might manage to deal their 2d6+6 hps damage the first round, that's not going to last very long, whereas a group of 20 1st level clerics casting Command, or worse, the group of 20 3rd level clerics casting Hold Person, will statistically cause anyone to fail their saving throws.)
My general feeling is that, if a PC manages to shore up one saving throw to an extent that a natural 1 would still save, I'm fine with them being invulnerable to that attack.