Hilarious iDenial. I guess returning one for said problem, and then watching them open two more new iphone boxes in front of me with the same problem, and then finally leaving with the fourth phone which then developed the same problem, was just... really bad luck! lolz
Design flaw. (see, I can use BOLD too) And the three iPhone 4s that my wife had to return because they were practically red hot all the time, never exploded. So your Li-ion fear is unwarranted, and incorrect.
And before you even try to label me an AAPL hater or whatever, browse my posting history.
First off I don't label you or anyone and Apple hater. That's just plane silly.
Second, it is quite reasonable that the battery supplier sent out a batch of bad cells in same lot that would make sense for as many phones to have bad batteries.
Third, I stand by the no design flaw statement regarding the phone. Any phone, any device will be destroyed if the battery is bad and expands. No device can withstand that kind of pressure unless it's a solid hunk of steel. So if you want to say the device is flawed in it's design because parts separate when large expanding force is applied, well ok by your daffynition it is a design flaw.
Fourth, I use Bolding, capitalization, and italics at times to emphasize the strength of my conviction about a point. If that offends you as it obviously does, well too bad.
Fifth, I won't waste my time looking up the article I read regarding a man being burned when his phone erupted in flames in his pocket. Or the article regarding fire onboard several aircraft, traced back to Li-Ion battery. But be my guest, carry a phone that is way overheating. I won't. But you and your wife can. Maybe you will be lucky and not get burned. Oh wait, you already mentioned you don't have good luck with phones.
Since you have obviously run into a batch of bad batteries, either wait a bit before replacing again so you get beyond that lot. By now I am sure Apple has gotten all over that battery supplier as I'm sure you didn't receive all the bad ones yourself. Plus if it was such a vast problem you wish to make it sound like. There would be major news articles regarding this "design flaw". There I did't bold it this time. How many millions of these phones are out there? But let's disregard that fact and focus on your anecdotal experience and globalize your hypothesis.
http://en.wikipedia.org/wiki/Lithium-ion_battery#Battery_life