Maybe the coins are like a fine wine..
Made me smile. I should point out that all my coins have a particularly fine bouquet
From what I have seen of ANACS, around June last year, a shift happened in the way they graded. Previously low end graded coins had the potential to jump +2 grades (although +4 is pretty significant, and exceptional). The higher end graded coins really only had the potential to jump +1 (+2 on very very rare occasions, as they have less room to be jumping into).
So the effect has been that the minimum grade has effectively increased by a couple. The maximum grade has seen a smaller increase. Thus all grades in between have been squeezed a little.
Even without the noticeable step change that happened in June with ANACS. Inconsistency is a problem that can affect all grading companies. The same coin recieving different grades when submitted multiple times is common place for the other big graders, as well as ANACS. But this realistically should only be +/- 1, and only then for those coins that are borderline, and the decision becomes subjective (and may depend on the kind of day the grader is having, what the weather is like, how busy they are etc). I am not saying that this is actually the case, just how it should be. The fact is coins are judged by humans, and humans are fallible.
Ultimately, while not perfect, grading is the best gauge we have for coin condition. Pictures rarely convey the full picture, and for a globally distributed group of people, a third party independant opinion is the next best thing to having the coin to hand (which generally isnt possible), even if its isnt consistent 100% of the time. Alongside that, always judge the coin not the slab, wherever possible (given the stated limitations of pictures, versus holding a coin and changing the angle of view to see the coin from all angles).