I. . .agree. D&D is a game of near misses. The orc attacks with his battleaxe, and hits your armor, your shield, the ground. . .but never actually cleaves into you. HP's would be single digits if that is how things worked. You might get nicked or sliced, but nothing serious.
I have a hard time seeing a *normal* character fall into lava and not die from the damage it would do to him, inside and out. Explain away high level characters with their magic armor and blessings from bahamut or whatnot, but if a 1st level Warlord falls into lava, he is not just going to be able to rub some dirt on it and be fine.
If a 1st level character falls into 'lava', he should be falling onto cooled lava. Something hot enough to hurt, but not kill. Or, just be a ruthless DM and make them dead. As long as everyone is on the same page going in, it shouldn't be a huge problem.
Jay