NewBie is absolutely correct (of course.) I have published a number of press releases for charger ICs and battery monitor ICs. There's no doubt that the technology exists to do this in a production light, and at very little added cost to the manufacturer.
The problem is the marketplace. The vast majority of flashlights sold worldwide are commodity items...relatively inexpensive incandescent lights that you find in all sorts of retail stores. Think about the more innovative manufacturers we see talked about here on CPF. One of the reasons you don't see products on retail shelves from some of the better (in our view) manufacturers is that they simply aren't mass-market items. In most cases, the manufacturers in question would be hard-pressed to supply the inventory volumes necessary for a major retailer to carry their products...regardless of the price of the light. Now add in that the average flashlight user considers a Maglite to be the upper end of the flashlight market price-wise , and you have some serious marketplace limitations.
For instance, we own a electric toothbrush that uses inductive charging (I think that's the right term) where the unit sits on a plastic stub to charge...no physical plug or direct connection. Yet I've never seen this approach to charging on a flashlight. (It doesn't mean they don't exist, just that I've never seen or read of one.) I know of no reason the technology isn't used in flashlights...except for cost. Our toothbrush cost $70.00. Most consumers would faint if they saw a $70.00 flashlight.
When general consumers begin to lift their price expectations for things like higher-end flashlights, and we begin to see more high-quality lights in retail environments, large manufacturers will be more motivated to innovate.
Right now, unfortunately, mass market makers are content with repackaging existing technology in neat new colors and shapes. And, IMHO, it will remain that way until the general marketplace demands more, and by extension, until profit margins make real innovation worthwhile.
Someday we'll begin to see things like monitoring ICs in production lights for the general public. But I doubt it will be tomorrow.