Intel is making a point to hit every market segment.
Intel's suggested pricing for the G620 is $64. G840/850 are suggested at $75/$85, respectively. I doubt an Athlon II can compete with them in performance - Sandy Bridge is just too far superior to K10. Even an extra core on an Athlon II X3 is likely unable to hold up against any SB-based CPU.
Intel's low-end offerings are a bit unusual, though. Sandy Bridge based Celerons are coming, and they aren't really being distinguished from the Pentiums in any way, save for price. It would've made sense for SB Celerons to be Hyper Threaded single core CPUs, while the Pentium would be a true dual core.