"Anyone of the old guard still remembers the 1985 Acorn Risc Machine, or, in shortform, ARM? The first ARM was 32-bit, just like its follow-ons 26 years ago now.
After staging a grand revival through the smartphone and tablet markets, and becoming the definite No. 2 CPU platform in the world, ARM has now set its sights higher, to the mainstream mobile, desktop and yes, even server markets. And that's where it hits the X86 leaders, Intel and AMD.
Now, ARM has no software base to speak of in the server field, and its architecture not only is still 32-bit, but also lacks all those error correction, reliability and durability features expected in servers. However, the application specific 'green' micro servers, used just for serving web page accesses, don't need any of these. They just require the ability to put hundreds of energy-saving simple CPUs in a single rack, each serving a group of web requests.
This a relatively small part of server market, and a low-margin one, an equivalent of generic corporate desktop in the PC market.
So, that X86 core consumes more power and die size than an equivalent performance RISC, so it needs to be compensated through system design. On the other hand, Atom is 64-bit from the start, keep in mind - an enormous benefit when handling any sort of shared memory mapping between hundreds of processors in a single server, something impossible for ARM for another 2 years or so. Not to mention all the X86 software support built over the years, something ARM will not have in foreseeable future.