Well, I don't know what happened with Greg's playtest or what he and Mearls discussed. I don't want to imply anything about someone else's experience.
I'm really iffy on how much I can actually talk about playtesting due to NDA and such, but, if I look at the recent Mord's book, for example, and go through my feedback line by line, they updated dozens of things that I reported as suspect. It made me feel really good - even if they did ignore me on a a bunch of things as well, and I don't like one of the ways they redesigned something

So, I could focus on the bad side, or the good side, but either way the process is doing something.
Anyhow, expect WotC to listen to our responses. The trick is, expect them to listen to folks who don't agree with you. And their own internal guys.
I remember when PF originally did its open beta, I objected on a bunch of things (many of which in hindsight were addressed), but I eventually gave up because their change intentions were too limited for me (a bunch of the spells still really bug me, frex). Giving up on joining the process, assuming I wouldn't be heard, means the final product is less useful to me.
So participate. Let's make this the best D&D we can.