Most sd cards are formatted fat32, and do not have a virtual filesystem cache and write scheduler buffering work in ram for them.

Also raspis do NOT like big fast SD cards with tight tolerances. I've had the best luck with old class 4 cards. Class 10 cards don't last nearly as long with regular power cycling.

You can force a partition to be mounted "synchronously", where writes aren't buffered in RAM and then flushed later -- every write blocks until it is written to disk.

The options are the third column in your /etc/fstab file. For example, if you had "errors=remount-ro", you'd change it to "errors=remount-ro,sync".

(Or is the Raspi problem actually in hardware?)

Did you ever run linux with ext2 (not ext3 or ext4) on a desktop computer in the early days? It used to fail spectacularly on unclean shutdowns. IIRC linux used to delay/buffer writes up to a minute or so. (Maybe it still does?)