A big factor is that the Ls7 cylinder block assembly includes pressed-in cylinder sleeves and forged steel main bearing caps. Pressed-in cylinder sleeves are used to allow the large 104.8-mm bore while the six-bolt, doweled-in-place CNC-machined forged steel main caps offer the superior strength required at the LS7's power level. The smaller-displacement LS2 engine (101.6-mm bore x 92-mm stroke) has cast-in cylinder sleeves and powder metal main caps.
You can do some more reading here:http://www.corvettemuseum.com/specs/2006/LS7.shtml
But that is the main idea. Its a lil different block than a stand. ls2 and with the use of coated and better parts like titanium rods, it is able to take the beating and not break easily.