Above a certain (fairly low) level, potions were not going to get your front-line characters back up to peak condition unless you were dumping gallons of potions down their throats. Whether it was due to loss of hit points or loss of per-rest/daily abilities, parties eventually had to rest in IE games. Pre-3E, clerics (or druids) had to devote a lot of their spell slots to healing. Some of those healing spells were used in combat, but often they were used between combat -- in essence trading the loss of one resource for another, but still accelerating the diminution of party resources. It also practically demanded the presence of a dedicated healer for extended exploration.
In 3E, the system ameliorated the necessity of loading up on healing spells by allowing good (and some neutral) clerics to spontaneously convert prepared spells into cure wounds spells of similar level. 4E took this a step further and implemented healing surges, which gave ALL characters much greater flexibility in healing themselves between combats, but gave them limited ability to do so within combat -- unless assisted by another character (e.g. a cleric casting healing word as a minor action). A party without a healer has a certain disadvantage within combat, but is nowhere near as disadvantaged between combats (compared to 2nd Ed. or 3E/3.5).
The Stamina/Health system is intended to accomplish a similar goal, but Health is still intended to be a resource that progressively dwindles down and encourages the player to rest. In PE, my belief is that this system will make that progression less chaotic and dependent on the presence of certain items/classes than it is in pre-4E D&D.
