I think 'encounter' vs 'adventure' focus is a matter of presentation though.
I think there's a pretty clear distinction. An Encounter is a scene. An Adventure is the chapter, or perhaps a whole book.
A scene is, usually, some set number of actors interacting with each other, essentially simultaneously. In a combat encounter, an XP pool helps ensure that the NPCs are balanced with the PCs.
But over the course of an adventure? Without assumptions on the distribution of XP (which Mike did not make, and it seems to be the point of his idea to not make), I'm not seeing the value.
As for XP budget for adventure, I already do that. In fact it is a well-discussed concept here and in other forums at this point, so not even notable.
But what are you getting out of that XP budget, aside from predictable advancement rates? Is it really getting you much in the way of building balanced challenges? Can you spread that XP across an adventure and be confident of a balanced challenge? Because that's what encounter XP pools get in 4E, for the most part. Follow the encounter building guidelines, use that XP, and as long as you don't do weird stuff with terrain, etc., it's quite likely that you'll end up with a balanced encounter. Do that with Adventure XP pool, and the difficulty will vary wildly between "big battle" adventures, and "a monster in each room" adventures. What is that pool getting you then? Are you making assumptions about the adventure structure when you use that pool?
Ultimately, a adventure XP pool is like an encounter XP pool, but only if there's an assumption that "wave" encounter designs are just as challenging, for the same XP, as "all at once" designs. That's obviously not true. 4E's DMG2 discusses wave design, and what it boils down to is that there should be more XP in the pool in an encounter with waves, but it's really a judgement call. That encounter pool gives a reasonable baseline for 2 waves, but past that, it's more DM judgement than rules. And once that happens, there's little point to having those rules.