OP, I'd ignor most of the responses in this thread, which you probably are anyway....
To answer your question, the sub didn't blow because it wasn't broken in properly, so don't worry about that.... as far as why the sub blew, it shouldn't have... but without looking at the sub and install no one here can say what happened... there is a good chance it was a defective sub... either shorting lead wires or a bad coil...
Let the shop take care of you, that is why people go to a brick and mortor shop... They sell it, install it, and if something goes wrong they are supposed to make it right... The buy online sack riders posting in this thread seem to miss the point that not everyone wants to DIY and may also want some face to face customer service...
Once the shop gets you a new sub, have them put it in and play the system before giving it back to you... If there is any doubt things are not setup properly you might want to take it by another shop to take a look, or call and talk to JLs tech support... If by chance everything is setup where it should be, and you cook another sub, there may be a possibility something is wrong with the amplifier...
Hope you get it sorted out..