Hmm... I think auto success/-failure for attack rolls and saving throws but not for skill checks is OK, though it is noch explicitly stated.
The argument that it always hat been that way, on the other hand, is not totally appropriate, because saving throws and skill checks worked differently in 2e:
Before, you had a set value for your saving throw (which started high and decreased in time), that was determined solely by your class and level and which you had to beat with your d20 roll. It was only a few cases that the caster / event that forced you to make that saving throw had anything to do with the success or failure (your poison save was, e.g. 12, no matter if a giant scorpion stung you or a honeybee).
A skill checks (and ability checks), on the other hand, was staying under your ability score (maybe changed by the skill), and here we your ability score was the important part, too, not the event or enemy: it was no difference in evading a normal fireball cast by a dumb mage (just intelligent enough to cast the spell) and evading a delayed blast fireball cast by a genius.
Now, both checks involve a d20 roll, adding a bonus/penalty from an ability score and another from your ranks/save bonuses. The result has to beat a DC.
In 2e, you be poisoned, and the saving throw for that would be something from 20 to 1 (maybe something exceeding that), basically the values of a d20 roll, and now, both the DC and your total roll (and even your total bonus) can be from minus something to 30 and (far) beyond. In 2e, you seldom hat events where values below 1 or beyond 20 would occur, anyway, so the auto success/-failure was a small thing. But now, you can have vast differences (a sickly Rogue1 with Con 8, resulting in a Fort Save Mod of -1 has to save against colossal monstrous scorpion poison, save DC 54). In 2e, this usually would call for a saving throw against poison, with success beginning at around 15 (I don't have the charts of 2e handy; grateful for every hint!), where in 3e you couldn't possibly save against that poison without auto success (your best shot would be 19, far below 54!)