It could very well simply be something that wasn't implemented - a purge feature. I'll bet money right now that it's coming though. Obviously because the issue has been brought to the mainstream.

None of this is an excuse for Apple not having been more forthright about this, nor for not including a method to clear/purge the data automatically/manually or turning the feature off entirely.

I believe the consensus at this time is that the data helps the device to save battery. Somehow.

My data is nowhere near as dense as some of the examples I've seen others post. No Oakville, barely any Mississauga, no Toronto, no Montreal, no Tremblant and nothing South of Burlington - all places I've spent significant amount of time connected to 3G and passing by wifi hotspots. And honestly, I've not spent any significant amount of time at the 407 and 400 where you see that cluster in Vaughan. At most, I can remember driving through along the highway in fact.