Also note, that there is DD-WRT, which is a similar, but different project. Some routers might be supported by one, but not the other. I have a Netgear Nighthawk, for example, which is not supported by OpenWRT, but by DD-WRT.
It wasn't the end of the world since a standard openwrt image could be loaded over tftp, but it was annoying that it was impossible to recreate the images available for download.