This is absolutely correct.
Unless it's something really extraordinary, like Jeff Willms' one-month kill screen (or Allen's 15,000 games with NO kill screen
), saying that it took "x" amount of time to reach "y" milestone really doesn't mean much. (And even at that, Jeff told me he put a LOT of hours into that month.)
I got my first DK kill screen in December 2011, almost 2 years ago, and I haven't hit a million yet, but that's because I really haven't played very much DK since then, certainly not relative to how much I was playing between October and December '11. I don't touch it for weeks, often months, at a time. I was way more obsessed about getting the kill screen than I am about getting the million!
So if I were to get a million by the end of the year, saying that it took me 2 years to go from kill screen to a million would be
technically correct, but really, what would that mean?
Hours played is the only way to get a meaningful gauge of a player's speed of progress relative to other players, but calculating that would require a great deal more attention and record-keeping than most would care to do.
Besides, I'm very much a fan of people NOT comparing themselves to other people...
To me, that's the beauty of the CAG stuff. It's not direct competition. Or at least, it doesn't have to be.