My initial reaction was also, interesting, but is there any point in knowing? A slightly random response follows:
Pools are held in the realm server's memory, and generated as the realm server is started. If the server crashes they completely reset (including the chance that they will reappear in different places).
Quite a lot of world information is held this way. Until recently, if the realm crashed during the Sunday Extravaganza, non-contest pools would re-generate on re-start, because even the event itself was held in the memory. The state of mobs (creatures) is similar: Probably the most fantastic sight in the game is the mass-submerging of all the dwarf mining machines in Storm Peaks, at the moment the server starts up - an entire field of neatly lined-up machines disappears into the earth. (Unfortunately you need a very unstable test server to plan to see that.)
Loot. The wisdom of EJ suggests that all loot is held in cascading tables - it's an efficient way of creating the illusion of complexity, while also being very hard for us to untangle. Same logic of "illusion of complexity" was applied often in the original WoW - for example, originally all of Azeroth's fish were determined by a 2x6 matrix, with a 4-stage time variation applied to 2 of the 6 zone groups (see Gazetteer) - yet that pattern wasn't broken until I started looking, almost 2 years after the game's release.
The best understanding I have of this comes from rearranging "bugged" stacks of herbs (it should work with ore to): There is a rare chance that a stack of herbs will simply not mill (via Inscription). However, if you gradually move 1 herb at a time out of the stack, into a new stack, there normally comes a point at which one of the stacks can be milled. This suggests that the outcome of the milling is determined by a calculation based on the entire contents of the stack, not simple that "you have herbs". That in turn implies that each herb carries unseen data, because the outcome of the process must always be the same (the initial failure of milling is consistent until the stack composition changes).
Before WotLK, there was an official comment revealing that creature loot was created at the time the creature was created. The specific example was for instances (dungeons), but the same technique would logically apply to everything.
However, WotLK introduced something I call progressive de-randomization of quest drops: The longer you farm for a quest drop, the higher the probability of the drop from each mob killed. After a certain number of kills, the probability becomes 100%. It ended those really annoying ("I killed 100 mobs - this quest sucks") grinds.
During WotLK beta a few people noticed that some of the really annoying quest drops had become less annoying, but I don't think anyone realized the method of determining drops had changed - that was revealed by Tigole some months later.
The change initially caused fish quest items to "drop" with 100% chance - something which I'd found in testing, and remained during the first few weeks of release. So fish were also altered by that change, but possibly in a slightly unusual way.
(It's worth adding that pre-TBC quest fish and TBC quest fish had previously been coded in different ways - one as a separate catch; the other as a catch alongside another fish, like we now have. Fish quest drops were programmed inconsistently, so more likely to get broken.)
While progressive de-randomization only applies to quest items, it is possible that all fixed loot tables are no longer as fixed as we might think. For example, the Dalaran fountain loot table changes based on the presence of a player-specific buff. In theory Blizzard can change the catch rate depending on what hat you have on, whether your faction controls Wintergrasp, or... any spell (even an internal "invisible" buff). And because all the fish drops are decided by the server, there is no way for data-miners to know. Fortunately that doesn't fit Blizzard's overall design, which is increasingly very clear about the factors influencing anything - which is probably why we don't see Variation by Time of day for fish in TBC and WotLK.
Why are loot mechanics changing?
It's probably the worse kept secret that Blizzard had serious problems with databases in the early years. As you might imagine, the volume of constantly changing data floating around WoW is immense. And write-intensive databases don't shard easily.
However, in the 5 years since, server capability has got 3 or so times better - very crudely, you can attach more memory to individual server machines. Which is probably why we're now seeing the evolution of things like drop rates - and more obviously achievements/statistics, or larger numbers of players supported on each realm: A game originally designed just outside the boundaries of the technology, is now comfortably within it.
So, where does that leave pools? It doesn't. I still don't know. But be wary, because what might have been the case a year ago, may not now be the case.