As I've mentioned at other points on this blog, the Palladium system is an advancement and refinement of old school D&D. One of those advancements was in the field of hit points. You see, before the 3rd edition of D&D all hit dice were rolled, even the first one. Which meant that if you were unlucky, it was possible to enter the dungeon with only one hit point.
Palladium starts you off with hit points equal to your P.E. score +1d6. Then gives you physical skills that can improve P.E., offer S.D.C. upgrades, and so on. Then armor provides its own pool of SDC (or MDC) to protect you. This means that your character has a better chance of surviving first level, which is good. But it also means that characters can very quickly wind up with unrealistic amounts of durability.
Stories circulate around the Palladium community of players exploiting this superhuman durability in interesting ways. Shooting themselves with assault weapons to intimidate a foe. Leaping on a grenade and expecting to walk away with only a small portion of their SDC gone. If you've got a fun story to share, feel free to drop it in the comments.
The important thing to remember is that, in D&D, hit points are an abstraction. They don't represent actual injury. D&D characters really only have one hit point (their last) and all their other hit points represent the character's ability to defend the one that matters. A friend of mine gave this concept a very clever name: "Ablative Awesomeness." When you make a successful attack, you're not hacking away at the other guy's spleen. You're hacking away at his ability to defend his spleen from later attacks. This is why experience (generally gained from fighting) grants more hit points.
The Palladium system doesn't seem to believe in Ablative Awesomeness even as it looks for ways to add more. The description of SDC in the main Rifts book describes a character taking an injury, but shrugging it off. The justification for increasing hit points as the character levels is that the character actually got tougher. Taking a hit in combat is apparently all about being a manly badass.
But with characters having all of these hit points and damage absorbing resources, the things that are supposed to kill them suddenly aren't scary enough. So you make up new stuff that is scary. In Palladium Fantasy, this is magic weapons, going all the way up to rune weapons. In Rifts, this is MDC.
But MDC adds a new wrinkle to this arms race. In Rifts, your MDC armor is your hit points. Without it, you are a 1 hit point mook. So as the weapons get scarier, you look to buy more powerful armor. Once you get more powerful armor, the GM has to look for tougher monsters and tougher weapons to fight you with. Leading to a little thing we like to call "power creep."
My current plan for BTR does include the potential for increasing hit points but nowhere near to the generous levels that Palladium provides. They will be available as a milestone attached to a character's combat skills. This should provide a balance, as there will be many other combat milestones to acquire as well. Playtesting will tell.