Honestly, I think this is just a simple case of adaptive tests doing what they do best.
I don't think anyone is tricking anyone, or purposefully trying to say its hard to "psych" the competition out. I think one very simple this is happening - the adaptive tests are being adaptive, and those that take it twice are seeing this.
That is, the only people who have the ability to provide any information on this subject are those that took it in 2005 and 2006. Generally speaking, what would you expect to happen to someone who takes the exam twice? Their score goes up right?
And how does someone score go up? They are getting harder questions right, right? So, by the very definition of how the GMAT works, you are going to see harder questions as you improve.
Therefore, all this talk of "Wow the quant was harder!", to me, is merely a reflection of people having studied or being less nervous and it only proves one thing - the GMAT is in fact adaptive.
Why dont you see that in the verbal then? It's harder to tell what is "easy" and what is "hard" in a verbal question. In math, if you get a basic rate and work problem, you can probably guess it's a medium question. If you get some crazy combinatorics stuff, you can bet it's not in the medium category. There's no way to know for sure, but odds are, a question like that would be considered more tricky.
For verbal, how can you really judge how much harder once sentence correction is over another? Would "Tommy enjoyes food like tamales and pizza" be a more difficult question than "Jodie and I went to the store along the street, which was dirty because the owner never cleans it." ?
So, I suspect the verbal is actually probably a bit harder in some cases, but because its much harder to tell if you have a "hard" GMAT question - you dont hear about it. I also think people tend to focus on the math side of things - I mean, if you don't know the ratios of a 30-60-90, you can learn, but if you don't know how to think critically, there isn't that much you can do. So, typically, I would expect that most people focus on math, and see the largest improvement there, and hence, the harder questions.
In other words, in my view: pay all this crap about it being harder no mind.
(That being said, this is purely speculation as I did not take the exam in 05, so I cannot compare.)