You also don't adjust the CR if a party doesn't have a wizard -- but SR 100 should factor into the monster's CR anyway.
Golems really don't have a lot of HP for monsters of their CR -- but they're supposed to be immune to Sneak Attacks and immune to all but a very small list of spells. With the huge variety of no-SR damaging spells, the latter defense has become basically irrelevant.
Most of the tougher undead (liches, vampires, incorporeal) also didn't have a lot of HP for their CR, since they didn't have a Con bonus.