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During Heroic I don't use a Glaive, as I don't have access to Polearm Gamble or Psionic Speed yet.
On the other hand Trantyr & Shield gives me a nice +2 AC & Ref until I get Talaric Ironjack, and I can use Swift Spear to prone with OAs already in heroic.

Swift Spear is retrained when getting to Paragon, as I need Polearm Gamble, HBO and ideally Psychic Lock ASAP.

Gold... That item is one level higher, and particularly during Heroic that's quite a difference. Furthermore I assume realistic item progression, meaning I don't switch stuff around willy nilly, but assume you can upgrade stuff only every so often - hence I stick with what I bought at L2.
Also... I'm a Dwarf, and I have Con primary. So before not being bloodied and having used my Second Wind as minor I sure ain't ask for a heal from the Leader...

No, not really a replacement.
1) I can't push the main target. -> Problem with HBO.
2) One attack roll, all or nothing. -> One missed melee mob is easily controlled as Defender, three Brutes going rampage are bad news.
3) Not attacking everbody means low damage as well as no rider. -> No like Psychic Lock.

We have enough PPs to spam some Bull's Strengths and still LR every now and then. Why not use them ?

Good and fair questions.

Rulewise you're correct about provoking.


Now regarding your actual question. Before I answer it, some important information:
1) I've ran the build in Paragon (even in the weaker pre-PsP version) and it worked fine. Of course YMMV.
2) While the number of reach mob certainly increases, they're far from the being the usual. (Check my monster handbook for numbers.)
3) There are ways to generate OAs and to often avoid being attacked even in melee. More infos below.
4) But complete melee immunity isn't the key. You're a Defender, and as Con primary you can take a lot of punishment. Threatening with worse fate, and making the mobs all go after you is perfectly fine (and still quite futile, as my DM learned).
5) If that isn't enough for you, there are ways to make you even less aproachable, even if that wasn't my main goal, as explained in 4). Again see below.

Concerning 3)
The build is very tactical, and it indeed needs a bit of time to be learned and played well.
The main idea vs melee reach mob is as follows: Push them, prone them, and end your turn 2sq (or just far away) from them. Now they can either stay prone, or they have to get up and charge, provoking another OA with possible push-prone. VS ranged mobs your main target, even more than melee mobs, is to herd them and rob their move actions, as they now lie adjacent to you, and are threatened by either another push-prone, or by a three target attack with Psionic Speed.
Furthermore the build rearranges the mobs how it suits your team best. In the process you deny them mobility due prone, and hand out debuffs (-2 psychic, -2 if they stay prone). You can get your allies out of trouble, or even make two different packs of mobs if convinient.
Furthermore the build is incredible mobile between his actual turns, employing Lightning Rush (even unaugmented - autoprovokes OA on ranged attacks) and Opportunity Sidestep. That can negate a whole bunch of actions for the mobs (either wasted or at good penalties and often vs yourself) - hard to grasp in theory, beatiful in practise.

Concerning 5)
First there's always the push 5 from your PP encounter - that plus just moving away means a turn done nothing for melee mobs.
There are other consistent ways. First you can take Repel Charge, so even if they charge non-adjacent after being prone, you can to use your OA - push-proning them, or just moving away thanks to OA Sidestep. Then there's always Headman's Chop to dissuade targets from staying prone (beyond the regular penalties). You can also take Proficiency (Gauntlet Axe) (from DSCS, possibly skip Hafted Defense for it) and as then wear a shield and still can use your hand to wield the Glaive, you can use Hindering Shield to push-prone-slow. At last push increasers help as well

I hope that answers your questions.

Well, I have quite considerate DMs (we rotate), who rarely provoke more than either absolute necessary or when really opportune to pile up on a weak target. Even the threat of "attacks three targets, shifts 2, marks & debuffs all targets" is pretty effective, because handing me even one chance per round (and I do get that if I want with Lightning Rush) means I can pretty much screw every mob in the vincinity.
Yes, your damage is probably only average Defender level, though indeed to multiple targets (and being open for tweaking with like Headman's Chop). But body blocking, debuffing, mob forced movement and attack redirecting make you a big PITA.

Body Double is certainly an interesting alternative to Psionic Speed. I tend to alternate between BS and PS on my OAs as I see fit, and I even use PS instead of BS every now and then (usually augmented). But your assessment is correct, BD can be a big asset for that build.
I think PS is still a bit stronger (and I'm just in love with all that mobility), but I'm certainly curious to hear stories about how BD works in play as alternative.