Its very common for major linux distros to have ARM builds. I'm just surprised because Canonical and Ubuntu are a lot more commercially minded than most Linux organisations. I thought when they abandoned Ubuntu Touch they'd probably lose interest in ARM all together.Always thought most (mainline) Linux distros had ARM counterparts to coincide with them.
Then again, I've gotten too adjusted to Arch to see that far into the others, but fairly sure it's not abnormal. The OpenPandora/Pyra projects certainly helped.
I suppose it isn't to surprising it exists considering debian ARM is the basis for raspbian.