I'm not an expert on LiIon, but I'd venture a good guess that Toyota might match cells in the NiMH battery pack. Mismatched cells cause a lot of battery pack failures in NiMH. Builders of satellites do this too. They need their packs to last a LONG time.

But I doubt that any cell phone maker would go to that much effort for a "consumer product". It would increase costs too much.

So I believe that there is a basic "quality" issue as well as good charge management that makes Toyota's pack very reliable.