I know you guys think sales aren't important, but if they continue to decline Morning Musume won't be getting on all of those TV shows, or the billboards or the commercials. Sales did matter when Morning Musume was at 40k because they were a reflection of the loss of the groups popularity. And they matter now because the increase in sales is a reflection of the groups rise in popularity. Also without high sales the girls can't top the oricon charts. They have been getting a lot of respect for topping those charts.
The sales only don't matter
right now because, sales are still up, they are still charting number one, and they are still getting tons of exposure. As long as the group maintain this level of exposure they can continue to take in more fans and make themselves well known to the casual fans. But the goal of all this promotion would have the affect of raising single sales. If the sales go down after all that it means that something's not working

And the only reason AKBs sales don't matter is because they can fart and sell it for millions. They are already at the top. They made it. Now they can sit back and enjoy the spotlight.
I don't think it's wrong for me to want Morning Musume to reach that same level of success. Sure I'm like you guys and will love them regardless, but I want the rest of Japan to love them too. I think with Sayu and the girls hard work they deserve it.
So in conclusion... I am a little nervous about the sales drop, but I don't think it's cause for concern just yet. As long as they stay steady in sales over the next few singles and do not continue to fall then everything is A-OK! But you can't say that the sales don't matter. They really do mean something.