Enki42:
The Linksys WRT400N uses the AR9002, while the
WRT320N uses the BCM4717 (4718's little brother).
Netgear has a single-band BCM4718 device on the way, the WNR3500U (may also be called WNR3500 v2). The DGND3300 also uses a Broadcom chipset, but the photo quality wasn't good enough to determine which one.
The D-Link 450 Mbps router is likely to be based on the
Ralink RT2883/RT2853 chipset.
Given that Atheros hasn't announced a replacement for the AR9002, and that the WNDR3700 is due this quarter, the AR9002 speculation is probably correct. Older platforms have used the AR7161, but it's unlikely Netgear would opt for them.