Re: $25 Ray-O-Vac 4 watt 150 lumen Cree changes everything.
Someone asked about C/D cell NiMH and why they are (effectively) only "repackaged AA capacity" cells. It's been discussed a few times here, bottom line consensus is that the retail, consumer-level, chargers on the market won't charge anything higher than that (some won't even charge up to 2500), and the demand for C/D cell rechargeables is so small that the demand for higher capacity chargers to use with larger mAh cells would be even smaller... bottom line, mass-market demand for larger cap cells, and the chargers to charge them, simply isn't there.
However you can find plenty of them online at battery specialist places, chargers and cells, that are much larger capacity (4-6k mAh for C, up to 12k for D cells, "mfger specs"). Of course you pay accordingly, 2 high-cap C or D cells are typically in the $15-25+ range, and a charger to fully charge them in one pass within a reasonable time frame is in the $50-125+ range usually.
Obviously the average consumer isn't going to pay over $100 for a charger and 2 batteries, so they keep the C/D cells at the consumer charger "limit" of around 2500mAh so that the $20 chargers can charge them up in less than a week, and they don't pay as much for the cells (although seriously overinflated, they should cost a minimal amount more than the AAs considering it's mostly empty packaging at that point).
Hope that helps.