Cost-down is the Watchword
Linksys' announcement of the replacement (yep, when 600N stock is gone, it's gone) for its popular dual-band, dual-radio draft 802.11n router has inquiring minds wondering what's different. So I did a quick dig through the FCC ID docs to bring you the answers. What I found is a design with a focus on cost reduction and ease of manufacture and some component changes, too.
Figure 1: Linksys WRT610N Simultaneous Dual-N Band Wireless Router
Figures 2 and 3 show the inside of the 600N and 610N respectively. Keep in mind that Figure 2 doesn't show the thick aluminum heatsink / RF shield that encases its innards. Check the 600N's slideshow if you want to see that. Early designs like the 600N and Apple Airport Extreme took a conservative thermal design approach for the relatively (vs. 11b/g) power-hungry draft 11n chipsets.
Figure 2: FCC photo of WRT600N main board
But those concerns seem to have been overcome, since all the current designs that I'm seeing take the more conventional spot RF shield and heatsink approach that you see in the 610N in Figure 3.
Figure 2: WRT610N inside view
A closer view of the 610N's board in Figure 4 shows the most of the component details, except for the switch chip under the heatsink. I'm guessing that it's the same Broadcom BCM5397 5 port gigabit switch used in the 600N, since the BCM4705 CPU is the same.
It looks like memory has been increased from the 600N's 32 MB to 64 MB in the 610N. A photo in the FCC docs that I'm not showing, shows a single Eon flash chip on the bottom of the board. But it's too fuzzy to tell whether flash has been changed from the 8 MB in the 600N.