> Another reason to prefer the cat variant is that it lets you actually string together a normal shell pipeline.

That's just as easy with dd, decompress|dd is especially useful:

xzcat linux.img.xz | dd of=/dev/sdb bs=1M

Throw pv in there if you want to.

> here are two ways to create a 100 MB file containing all zeroes

And here's a better way: truncate -s 100m zero.img