I don't know if you could say there was a specific "Wrath Model" though. Sure people use the term to refer to things as being generally easier, but in terms of raids? Wrath was highly experimental and aside from Halion, every raid tier was different in terms of general mechanics.
T7 we had inklings of hard modes with Sarth 3D and some of the achievements, but for the most part it was similar to the way raids worked previously (single difficulty for boss), with most fights being undertuned compared to what a "normal" tier should be like.
T8, Ulduar, still hasn't been topped IMO not just for the bosses/environment of the raid dungeon, but the methodology behind the hard/heroic modes and tuning. Tuning on normal mode encounters was good, and hard mode tuning was great as well. Some fairly easy hard modes, with others being challenging, but doable, and others brutally difficult (perhaps overtuned.)
T9 - Quality of the raid instance aside (the bosses themselves weren't actually that bad - just other things about it...) we now simply have a UI toggle for heroic modes, like you would have for dungeons. This isn't as fun and doesn't allow for sliding difficulty like was possible before (Sarth, +1+2+3, Freya + Elders, Iron Council, etc.) I don't think anyone ever disliked having more ways to tackle a boss.
T10 - Here we carry over from T9 pretty much, a more refined version of that system, except now you don't have to run the instances 4 times in a week since doing the normal or heroic mode locks you out of the other (you can only kill a boss once per raid size per week, rather than twice as in T9).
T10/T11 - Same as T10, except now you can only do the raid once per week (one raid size.)
I may be leaving some specifics out - they did so many changes during/after T10. In T9 you just switched the entire raid instance over to heroic, but in T10 it was toggleable per boss at one point? Then it wasn't? Anyway...
Point is...they tried out a fuckton of different things in Wrath so there is no "Wrath Model" unless you just mean a general lack of need to CC - which did exist in some spots, but was outgeared much quicker than seems to have happened in Cataclysm.
Ulduar with sliding difficulty for some bosses and binary for others was still the best overall system, but I remember Blizzard at the time saying that they chose not to continue doing that and went with the UI toggle because the options "were too confusing for players" or some such bad explanation. That argument wouldn't hold water now with the introduction of the Dungeon Journal clearly pointing things out for you. It would be easy to put in the details that say "Oh, killing XT's heart will activate his hard mode and make him stronger, he now gains X abilities and loses Y abilities."
Another reason could be - you have to design better encounters for sliding difficulty to work (again, it doesn't have to be on all the bosses, but still...) and coming up with mechanics that activate a hard mode as well as hard mode mechanics themselves would become too difficult over time, so Blizzard just scrapped it for the toggle we have now that gives you the trio of more health, more damage, a couple new abilities (and possibly more for showpiece encounters like Ragnaros.) That's the pessimistic view though - that they decided to take the easy way out rather then stretch themselves with good design.
So if you got anything out of this post...
Yes, 2 years later, I'm still bitter over patch 3.2