I always wondered about this since I haven't had any issues with the devices listed (on Yosemite): Mid 2007 iMac, Late 2008 MacBook, Early 2009 MacBook, Mid 2009 13" MBP, Mid 2010 15" MBP, and my Late 2013 13" rMBP.
BUT, I took delivery of a brand new 2015 MacBook Air two weeks ago, i5/8GB/256GB with Yosemite preinstalled (10.10.3) (everything else was upgrade or clean install) and it doesn't connect about 90% of the time. So I have to toggle it off and on to get it to connect again. So this is an issue, but it doesn't seem to show up on every device. But for one that has been doing it since I took it out of the box with zero software installed by me I will say that it can and does happen. I have seen it a few times on my rMBP and the 2009 MBP intermittently. But not nearly as often as this MBA.
I do remember this happening on the Yosemite DP and betas and even up to the final release in which I went back to Mavericks on my rMBP until a couple months back when the .3 update came out and I went ahead and upgraded. Our iMac won't stay asleep since the update with no other changes too, but I don't think that's related and I'm wiping it when El Cap comes out anyway. The thing has been upgraded every release since Tiger!
So yeah, it does happen, just not on every Mac.
Oh, and it does this on all networks, not just some. I've got an AirPort Extreme at my parents house, a crappy AT&T modem/gateway/router deal at the place I'm renting, an enterprise class UniFi AP network at work that I've been setting up along with a few AirPort Expresses in adjacent buildings and the MacBook Air doesn't reconnect to any of them after waking from sleep. Sometimes it will, but only if it's been asleep for a short moment or hasn't left the building. This is a mix of 802.11g, n at 2.4GHz and 5GHz. So that doesn't seem to matter either.