In the previous version, they specifically felt the need to include language that allocated the temp hit points after the attack against the battlerager was resolved. No such language is present here. That may or may not mean something. It may mean they meant for the HPs to be granted immediately after the hit. It may mean there is something in the language of the ability that means something to the author or editor that makes it unnecessary or redundant. It may have been removed due to formatting restraints on reprints.
Well, the reason for the original wording about the thp only coming into play after the attack was fully resolved is to make it clear that it does not mean you gain the thp before taking damage from the attack (and they can't just say after taking damage as there are some attacks that deal no damage, as well as fighter powers that can reduce damage to zero, not to mention resistances and the like that come from items, powers, race that could all make for being "hit for no damage".)
The question is ultimately "when do you get thp from an invigorating power", as basically battlerager gives thp in addition to any thp you would normally get, which would imply you get it at the same time that you woud normally get the thp. The problem of course being that the
exact timing has never come up before as it wasn't really that important to know ... as they could be effectively simultaneous without really triggering any special conditions previously.
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Other points:
Basically, the extra damage is split into two things:
(a) Is the change into chain armor worth the slight damage increase? Now, part of this question is going to be how
bad does the AC drop matter for your party. For some parties, it may make the fighter a better defender to drop his AC a bit more and make a more tempting target. A chain and heavy shield fighter has the same AC as a plate and two handed weapon fighter basically ... so the damage increase needs to be comparable to wielding a two handed weapon to be worth it (which would require the "gain thp before resolving damage thus getting +1/+2 nearly all the time to make it good).
(b) Is the choice of an axe or hammer a good choice? In this case, it's a valid choice even BEFORE you consider your armor. Yes, you lose out in accuracy. However, you get to use your constitution synergistically with the various fighter powers that work with axes and con. STR/CON also works better for qualifying for the axe/hammer feats. There is Brash Strike that makes up for the attack roll deficiency and gives you extra damage for having the high con. If, for whatever reason, you were fine going in chain, the extra damage from wielding an axe or hammer is just icing on the cake to the other benefits of wielding an axe or hammer.
The chain armor thing seems to be an artifact of what they had originally. The tempest fighter gives up some AC (maybe not, especially if he has a good dex with his hide ... it can be as good as scale easily) to get more damage. The
old battlerager not only didn't mind scale as much, they wanted to be easier to hit so they'd be more likely to have thp to use the damage boost. This version is making it easier to lose the thp in order to get a conditional bonus that requires he keeps the thp.