It's not about performance per clock, guys, it's about performance per watt. ARM exponentially kicks the crap out of Atom on performance per watt (or any other architecture). For that matter, Core2, PhenomII, and Core i? all kick the crap out of Atom on performance per watt, Atom has exceptionally poor performance per watt.
When you look at a diagram an Atom die, the CPU core(s) take up most of the die. Now look at an ARM CPU, the actual CPU core is only a tiny part of the SOC. They could easily throw 8 or 16 cores into one of those and it'd still be smaller than an Atom dual core on the same node, which is why ARM is having no trouble scaling their cores and clocks up.