Sorry Elric (and Rovin), but I don't see what's so difficult by just adding in one or two extra minions for every four there is in the encounter, without them yielding any XP or changing the encounter budget in any way.
Seems like something that doesn't need a full-blown response to me. You simply add in a few minions; everything else stays the same. Easy.
This is just a "stealth XP reduction": give the XP for four minions, but where you used to use 4 minions instead use 6 of them (at epic). How would you know to do this other than this sentence in the DMG?
If you saw an encounter with 3 level 30 regular monsters (19K XP each) and 12 level 30 minions (4.75K XP each), should this be
1) a 114K encounter (Encounter level 31), which is what you get if you add the monster XP? Or should it be
2) 95K XP (Encounter level 30), because this line in DMG 2 indicates that 1/3 of the minions are "free" and don't count as adding a challenge or adding XP?
There's just no way to make published products coherent under this second standard (indeed, E3, the most recent epic adventure I've seen, simply adds minions XP in normally). The XP/EL totals on epic level encounters containing minions wouldn't add up, and unless DMs had read this one passage in DMG 2, they'd have no idea why. When a DM created an encounter like this, unless they'd read this one passage in DMG 2, they'd still treat it as 114 XP, EL 31, and so on.
Edit: It may be unclear, but my concern is that the lower value of minions needs to be reflected in the XP system for encounters to balance correctly. It's not about the pace of leveling.