If a noobie is running with a couple hi-caps, chances are their batteries are the in-the-box ones (i.e 8.4v 1200mAH). It wouldn't last that long if they just full auto it the whole time.
But theres a different story. Some mid caps EVEN high caps are hard to find for specific guns. Take a look at the G&G/CA M14 mags. Mid caps are out of stock everywhere, and the only place I seen high caps in stock for these are at eHobby, where they sell for $30. $30 might not seem much off the bat, but including shipping of $10, and waiting 2-4 weeks for it excluding customs fees, does that seem fair? Mid caps are the same story, but they have been out of stock for more then half a year. I would rather run 1 high cap that comes with the box, then 3-4 midcaps of $30 each (also the time it takes to wait for them to be in stock + being delivered).