They aren't competiting on price
They are just lowering the cost so that more people will accept per 50GB overages. I mean seriously would you pay $300 a month for a service with a 300GB cap and $10 per 50GB overages? I wouldn't I mean it's already horrible that for that cap you're paying almost $1 per GB anyway, gah when will people wake up and realize how screwed they're getting?!
Edit: Before people start saying "You pay that price because of the speed, not the cap!" You're paying for both.... 50 cents per GB, and 50 cents per Mbps, what a sad sad world, personally I don't even considering it paying for the speed when a cap is involved, because if you have to pay for overages, the best bang for your buck is when you get a larger cap for higher prices, not faster speed, people get this for their wireless smart phones, but not landline?!
Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning. -Albert Einstein