Or maybe 30 HD over 30 levels is actually the peak of PC hp inflation. You know since 30 > 20.
Sure, Epic level 3.5 characters could accumulate 30 HD.
[sblock="off topic math"]Though, even if we compare 20th level 3e PH1 to 30th level 4e PH1...
3.5: 20th level barbarian, 20d12 HD + 18 CON, 24 CON with a +6 item, 30 CON when raging: 216, 296 up to 376 hps, on average, with maxxed out CON and rolling all 12s, 500 hp ... before Raging for another 80)
4e: 30th level Fighter maxxed out CON: 219 hps, no rage available, but if a max-CHA Warlord were to use the Heart of the Titan daily on him he could gain 64 temp hps.
5e did rein things in compared to 3e: a 20th level max-CON barbarian only averages 236 hps, 340 rolling all 12s, and rage doesn't give him more... it just halves the damage he takes.
OTOH, minimum hps definitely 'peaked' in 4e. A 30th-level wizard with a 10 CON (you couldn't start with less than 8 CON, and gained 2 automatically over the first 21 levels) had 96 hps. Roll all 1's on your HD, and a minimum-CON wizard in 3e, or 2e, or 5e, gets 20 hps. [/sblock]
Turns out that people dont like their characters to die. Who would have imagined?
Heh. Though I suppose that may have come as a surprise to whoever had the bright idea of reducing 1st-level hps so dramatically. (There's somewhere you can hang your 'inflation peaked in 4e' hat: 1st-level hps definitely were higher in 4e than they are in 5e or are in any prior edition, for that matter, or PF, AFAIK.)
[sblock="off topic math"]
I guess since BAB maxed out at +15 then all those Monsters with their defences in the 50s must have been safe from those pesky Adventurers with their puny +15 to hit since that is the only thing that affects your attack roll.
+15 + STR + prof + weapon talent + Enhancement/Inherent + feats + power + Combat Advantage is a lot of bonuses. Not nearly +20 + STR (+ enhancement bonuses to STR) + size modifier + feats + Enhancement + Circumstance + Competence + Insight + Luck + Morale + Sacred/Profane + Epic... 3.x was just a lot more open-ended when it came to bonus types & stacking. It could get pretty crazy.
Plugging just insane absolutely maximized values into those would look something like:
+15 + 10 + 3 + 1 + 6 + 3 + 10 + 2 = +50 (but that's including an equally maxed-out Warlord blowing a daily to help you hit), so more like 40.
vs
+20 + 13 + 8 + 3 + 5 + 4 + 3 + 20 + 3 +4 +2 + 5 = +89, but that's including a True Strike item and scads of typically-silly high-level pre-buffing, so more like 50 on a regular basis.
Though, that doesn't count depriving your foe of DEX bonus to AC, or the possibility of stacking untyped bonuses...
Removing cheese brings that down a lot faster for the latter, though. More like 34 vs 43 [/sblock]
Not that 5e didn't (over?) react to the high numbers of the previous two editions, just that 4e had already pulled back from the crazy optimization-fueled excesses of 3e.