Pent, I do understand where you're coming from. I understand that a long, boring camp is a long, boring camp, made ever the worse by the are Madexx is positioned in and the random chance of his spawning. Personally I find it very very difficult to believe that in 9 weeks of camping a green has not spawned (or only one has) - RNG, yes, but that's, what, anywhere from 63-100 Madexx spawns (at one to two spawns a day) with only one of those being green? RNG doesn't work that way. Of course that's not your fault, however you must be missing spawns, and it's very probable green has been spawning and you're missing it. Which makes the issue less of a "Madexx spawn is fail" and more of a "wrong place at the wrong time", which really... isn't Blizzard's problem.
The issue I have with your argument is this. Rare spawn pet. Scorpid. Nothing special, many others in game (essentially the only thing you want the green for is its colour and model; aka vanity reasons). Annoyingly painful to track, but doable. Should it be made easier to get?
... Aeonaxx/TLPD. Again, the only reason people want them is either for the joy of having a rarespawn (in which their pain is self inflicted) or because they like the colour (vanity reasons). Both of these guys have approx a 1 in 16 chance of spawning with their more common counterpart. How is that different from Madexx? Should these guys be made easier to get too?
Same can be said for pretty much all the spirit beasts. For the achievement rares in Northrend and Outland. Like you said: how hard is too hard? Is appallingly bad luck on your part truly "too hard"? Is something on your server broken (which, if you had documented 63-100 non green Madexx spawns, I think you could safely say that there was a bug).
Sure, there are plenty of people who don't have the time to hardcore camp their chosen targets, but that doesn't mean it's impossible. Many people get their rares from random flybys or else logging in and out at a spot and checking late nights and early mornings. Heck, I got Aeonaxx last night after casually camping for maybe 8 hours total over two days (I admit I was INCREDIBLY lucky but I feel Aeonaxx and TLPD to be on a different level to most rares), purely from chance because I needed to go out during the day. For those who genuinely don't have the time, there are common counterparts which generally "will do" until they do happen to get lucky.
I suppose, from the above, I'm in agreement that this is more of an issue about YOUR horrible, long, painful camp and overall bad luck (and I really am sorry for that btw, it's cruddy regardless), as opposed to a system Blizzard put in place with the idea of satisfying all those people who said they wanted something different. Atm it seems hunters are getting almost anything they want thrown at them, and in a way I really don't like that. While WoW is a community driven game, sure, I feel atm Blizz is almost bending to the community in a desperate bid to keep it happy. It's not going to kill anyone to have to camp or whatever. Soon there will be no different/interesting-tame pets left because the community has said "this is too hard" or "this is too RNG" or "I don't like getting groups together" etc... what about those people who still enjoy the challenge of all the above? But they don't get a say because, well, they can put up with it, everyone else wants a simpler game. ^^
I also honestly feel, that if you're spending 9 weeks "hardcore" camping a spawn with no luck, that perhaps you should take a break. But that's entirely up to you. Come back in a few weeks and he'll probably spawn within an hour lol. That's how it goes.
Having said all that, though, I do quite like Kormai's RNG-structure idea.

If anything was to be implemented I'd find that quite reasonable and hopefully more encouraging for people who wanted to camp, without making the camp too "easy" or whatever for those who enjoy the random flavour of Madexx. I'd also be fond of the idea of adding in a new colour for the common scorpids and make them brown/new colour changers or removing the brown commons altogether.
But in general, Pent, that's why I'm inclined to disagree with you - I hope you don't think my opinion is unreasonable here, and really, Blizzard will do what Blizzard will do. I really feel your pain, and I'm sorry your camp is so long and painful, nor do I think it's cool you've waited this long. I just think there's a fine line between bad luck and genuinely lame RNG. ^^