Agreed that carefully written, standards-compliant apps that go the extra mile to avoid data loss regardless of operating system will have a portability advantage over most. But unless there are lots of users out there running on filesystems with weaker semantics than ext3, the advantage isn't that big.
Also, what the most carefully written apps do isn't particularly relevant to what the filesystem should do. The choice for filesystem writers is:
a) implement just the bare standards, and most people won't use your filesystem because their apps lose data, even if it's faster.
b) implement nicer semantics so that people will actually prefer your filesystem over others. Decreased data loss after a system crash, even for poorly written apps, is such a feature.
It's the same tradeoff that exists for people who write web browsers. When the standards are too weak to achieve compatibility with most apps, you have to go beyond them. You need both good performance and good compatibility.
Without this patch, ext4 would not be competitive with ext3.