The scenarios:
1. Apple responded to complaints.
2. The change is merely coincidental.
The complaints are the the evidence. The most logical answer is usually the right one.
Also, Apple is actually responding to design complaints submitted by developers. In some cases, they even follow-up with questions. Under Steve Jobs, Apple did not dignify such complaints with responses.
Well I only ask because 9to5Mac said certain items in beta 3 were already floating around during WWDC. And seeing responses here since beta 3, it seems a lot of people liked the thinner font so I'd be curious to know how many complaints they really received.
But hey, if developers are saying Apple is responding to complaints then I think that's great. I don't agree with design by committee and don't think Apple should be designing based on random iOS user suggestions but it is good to hear that they are more responsive. Maybe that's also a result of Scott Forstall being out of the picture.