Re: If voltage regulation is so great, why don\'t Surefire, Streamlight et al. use it?
I don't think there are very complicated reasons.
I think SF typically doesn't do it because the Li batteries are typically "good enough" for their purposes.
It's my bet that SF might get around to this earlier than others tho - one interesting thing is that it appears for some of their lights they engineer the battery and lamp solutions very close to the edge -- something that having good voltage regulation might make easier. It would also make it easier to mix and match battery and lamp options.
I don't think reliability or single point of failure is the reason, reference most regulated lights are for spelunkers. They of all people need something bulletproof (smashing it up on rocks, etc) and they rely on the light a lot.
Part of it may be cost and complexity vs reward. I think until consumers realize what they are missing and demand a better product, the manufactures aren't going to bother. Why make sophisticated device when we can do something simple and make just as much?
Note again that the most demanding and most informed consumers are starting to go that direction, reference the Arc AAA/LS, HDS Actionlight, Photon Fusion, various headlamps for spelunkers, some bike lights, etc.
It's also going to hurt manufacturers in some ways. Arc AAA vs Photon, the Photon can advertise a much longer runtime. If they regulated, the runtime would be much shorter - which would provide an oppertunity for inferior products to win because people don't know better.
The average consumer is going to plunk down $19 bucks and get a Maglite if they want a "high end" light! Or maybe they will just get that yellow plastic 2D one for $3.95.
-john