I wonder if this data is coming from when they introduced the two reports a week limit, which dropped the volume of my reports by 90% on it's own, or if it's coming from when they introduced the new (and hilarious) mute/low priority system. Or maybe it comes from large numbers of people just giving up on reports doing anything at all.
Basically, I smell bullshit on this one. Far more likely explanations for why report volume dropped than a simple question that no one pays attention to anyway.
Also, I can tell you as someone who play a LOT of dota2 (2k+ hours so far) that game quality has not improved at all since 2010, when I first got into beta. In fact, it's just gotten worse and worse with each new "fix" for matchmaking they introduce. Couple that with the total lack of content releases (still no where near hero parity with DoTA 1) and the fact that thousands of bugs still sit in the dev forum completely ignored for years...
Oh, but don't worry. Valve makes sure to release new hats every week