Of course, that isn't much of a rumor. Every iteration of Apple products is expected to be lighter and thinner. However, in this case the rumor pertains to the sides of the device actually becoming slimmer. The thinner bezel seen on the iPad mini is expected to be incorporated into the full-size iPad's design. Presumably that also means the larger iPad will be getting the software Apple implemented on the iPad Mini to prevent fingers near the bezel from registering as legitimate touch commands.
Apple Insider's source for the report is an analyst with KGI securities. The analyst also expects the new iPad to be released in the third quarter of 2013. That's a much more conservative estimate than some analysts, who have pegged the launch of Apple's refreshed product lineup to early or late spring.
Other 2013 Apple predictions from the analyst include an iPad Mini with Retina display and the unveiling of the iPhone 5S. Also, the long-rumored Apple HDTV has fallen off the radar for 2013. No doubt cable companies' stubbornness when it comes to unbundling their channel packages prevented Apple from creating something that could truly change the way most people watch TV.