“...because the infrastructure is denser and cheaper, you just don’t notice...”
This is my point. It is actually cheaper to cover a given area with wireless than it is a physical cable infrastructure. A $100K of equipment will cover 10K homes even in a rural area like Pahrump. That is nothing compared to the cost of actually stringing cable to each home on each street. Cable modem data usage is unlimited and that is who they need to compete with when it comes to users that want unlimited 3G/4G. You say “mobile” but that isn’t really the issue, is it ? Unlimited data is not going to be an issue when people are actually on the move. It is the tethered use while people are at home or at their office that they are afraid needs caps on usage.
Yes, the problem is mobile users, both the sheer number of them as well as their data demand growth. Think about what's next on the horizon. Every vehicle with mobile IP constantly exchanging data. Pandora radio in the front seat while the kids stream Netflix movies in the back. Video chat everywhere as texting is viewed as something akin to Morse code by the young. That's where we're heading and all of this is technically doable today--except for the lack of sufficient mobile bandwidth which needs to grow at a furious rate to keep pace. Metered usage is what will help fund this growth.