They are costly indeed, for the same reason "original" thinkpads or MBPs are costly: they're worth it.
As to "heavy", I linked to "business rugged" series of toughbooks. Fully rugged toughbooks (those you see on field work) are built like tanks and heavy as fuck indeed (e.g. Toughbook 19 with 5.1 lbs or Toughbook 31 with 7.9 lbs), these are much sleeker machines: way above an average laptop, but not MIL-STD or IP65 by a long shot.
The SX2 is 3.1 lbs. By comparison, a 2012 MBA is 2.38 (11") to 2.96 lbs (13"). Would you really call 3.1 lbs "heavy"? Let alone "extremely" so? (the C2 is a big bit heaver at 3.6 lbs, as it's a convertible tablet with a bunch more features like hot-swappable batteries)