Though it is a subjective opinion and not a proven fact

, I do agree—unfortunately—that the GMAT is becoming tougher over time (both the content and scoring curve itself). Thus, it has become even harder to score a perfect 800, which requires answering all 58 counted questions correctly on Quant and Verbal.
As further evidence of this claim, the only verified 800 we have here on GMAT Club (despite approximately 1 million members) is from 2015: a score that is no longer valid, because GMAT scores expire after 5 years.
One should also note that a GMAT Club
score verification feature has been available since 2017, covering GMAT scores from as far back as mid-2012. In other words: after nearly a decade of official GMAT scores, we have seen exactly one verified perfect 800.
There are of course those out there who who earned their perfect 800s prior to mid-2012, and those who have chosen not to verify their 800 scores (I know one of them personally), but I doubt that there are many people in this category, and surely fewer students than GMAC claims. The official number is .02% of test-takers, or 30 out of every 200,000, but I suspect this figure to be far lower in reality.

On the other hand, as you noted, there have been several verified GRE perfect scorers here on GMAT Club and on GRE Prep Club over the last few years, which supports the conclusion that it's easier to score perfectly on the GRE—especially with no lifetime limit.
Another important fact to consider is that on the GRE, you don't truly have to be perfect to earn a perfect score: you can earn a 170 + 170 = 340 composite with up to 4 questions incorrect out of the 80 counted questions (3 on Verbal and 1 on Quant).