There is, of course, the aspect of software. The article states that some software vendors, notably Red Hat, is doing a port for ARM. But which ARM? The aspect that ARM is licensed to device and semiconductor companies means that there are a bunch of different instruction sets out there so that something that you use on one ARM architecture implementation might not run on another.
OTOH, with x86, you just have to deal with Intel and AMD and they generally work together at some level to try to maintain compatibility.