Completely agree. It is rare to want to mount the image other than
booting the USB stick, so as long as that has lzma support, it's not
really an issue.
If you're talking about LiveUSB images, people mount them all day long
to make changes or modify them. I would assume though that for a
pre-compiled image all you want to do is write it and boot it..
otherwise it isn't rare for images to be mounted by hand.