> there's no fundamental problem in achieving feature parity
Sure, but if you're going to make that argument, all software is equivalent, because you can just implement the stuff you want and delete the stuff that gets in the way.
This is not entirely true for proprietary software :)
In fact, OSM is perfectly capable of representing lane restrictions (http://wiki.openstreetmap.org/wiki/Lanes) and some of the existing OSM clients (such as OsmAnd) offer 'lane assist' (arguably, it might not be as good as Google's but there's no fundamental problem in achieving feature parity).
And while the GMaps feature of offering you route alternatives based on the current traffic is nice, the "price" you are paying for it is unconditionally sharing your location with google while the GMaps app is running (or even at all times, depending on you settings). I personally don't feel comfortable with that compromise.