To say that any period had a higher standard as any other, is nonsense.
Today, we have obviously a different ideal than before. Thesis/antithesis - It's really not complicated.
If you listen to the really early recordings from the 20s, you'll hear wrong notes all the time. Was it because they were unable to play the right ones? Obviously not! They just didn't see right notes as the first thing to think about. If you listen to them, you'll hear that the imagination and "feeling" (to put it like that) was much more important.
Going a bit later, say 50s, I guess they got a bit bored with tempo changes all over the pieces, and that every new phrase should have a new feeling. So, they did it a bit stricter. Maybe the first and second theme needed different tempi, but not much more than that.
Now, or ideal is, in a way, more poetic. Tone color is very important (on I side note: You can find videos on youtube, where students of Liszt is playing. And if you listen carefully, barely no one do a proper voicing in the chords. Obviously they were able to, but they just didn't see it as that important. At the same time, you will never hear such a wild, say, Mazeppa from pianists today), voicing chords in the correct way is important, changing color in different phrases is important.
Also, the pianists of the early recordings could easily have met (or met someone who met) the great composers. If they didn't play up to standard, I don't think, say, Liszt would be very shy in telling them how much they sucked.
If Faulty_damper doesn't agree, I would love to hear your side of it!