Actually, someone corrected me on another forum. The Socket 423 Pentium 4 was bigger! Do keep in mind that Nehalem is no longer a square processor, one side has been elongated just slightly. It doesn't show very well in those photos. Intel processors up to thie point were always a square package.
This is the size of the processor package, not the socket:
LGA 775 = 37.5 x 37.5mm
LGA 1366 = 42.5 x 45mm
Socket 423 = 53 x 53mm
Socket 478 = 35 x 35mm