No, no one is saying that ZFS is more prone to defects without ECC. Lack of ECC increases the risk of corruption for any filesystem. The reason you hear more about ECC in the context of ZFS is that data integrity is a key feature for many who choose to use ZFS.

I don't understand why this is so often misunderstood.

The parent poster already stated the opposite.

ECC and ZFS are orthogonal. ECC ensures that data in your RAM is not corrupted (or rather detects corruption) it helps whether you use ZFS, EXT4, NTFS etc.

ZFS increases your data safety whether you use ECC or not, but if you have to have maximum assurance that data is fine you should use ZFS and ECC.

No, all are equally prone to errors if a bit in RAM is unexpectedly flipped. My understanding is that ZFS requires more RAM and possibly more CPU than other filesystems and those costs aren't worth it if you're going to use RAM that can't detect errors anyway.

To answer your question: No.

They are all just as prone to defects.

They do. There are now Xeon E3 notebooks that have ECC. It's something new they added with Skylake for that reason. They're designed as mobile workstations, so you're gonna be looking at at least $1700 for a laptop, but good quality's always expensive.

ECC is just as important for EXT4 and NTFS as it is for ZFS.