Battery life for lithium chemistry batteries is 2 folded into one. Overdisharge will cause the battery to last less and less over time, before you have it on the charger, full charge, and the battery will last a small fraction of the time it lasted when new.
Also, it really is not a safety precaution. My battery will get hotter than hell while working mid to low charge (not due to charge, I just work out the phone once and awhile.) I've done the same thing at low charges, it isn't good for it, but it happens. If manufacturers built a phone with a battery that would last a day none of this would be a problem.
I don't really know when those batteries exploded, but I want to say it was overcharge, blowing up on the charger or soon after taking it off the charger.
At least 4 things will crap out a lithium battery. Charge rate too high, draining the battery too low, and over use causing extreme heat, or a puncture (more likely in LiPo's)
Usually it takes a puncture or dead short to shoot off a LiPo, but overcharging at a high amperage will set one off as well. Because pretty much every battery in a phone today has circuitry to prevent overcharging, as well as to control the charging profile, because it is very sensitive. Typical LiPo at 30% (recommended cut voltage) will have a very steep voltage curve in the next 10-15%, bringing the battery close to final voltage. Time to full charge the charger is working like crazy, charging for a bit, then cutting voltage, rinse and repeat until the downward spike with no voltage is very close to the voltage of a fully charged pack. To give an idea about the power of these reactions, I nose dived my helicopter into the ground and just happened to puncture one of the cells in my 3 cell 2100maH 25c pack(2100maH is capacity of pack, 25c times 2100maH = 50 Amps being disharged almost all at once). I did this early in the flight, and my heli basically melted, as well as melting into the asphalt. But it did look like the Fourth of July!
Check out YouTube to see some idiots blowing up LiPo's so you don't risk your life or house or car, because they act like rockets.
Sorry about any spelling or grammer errors, up in the dead of the night.Hope I shed some light on the delicate nature of Li ion, and LiPo's.
Steve