iPhone 4 charging the battery to 100% and then completely running it down

So what I want from this thread is to understand some things regarding the iPhone 4 battery. Since I came from an Blackberry Bold 9700 almost all the users said that the BB can be left over the night to charge and it will not overcharge, and the most important fact is that it is recommended to charge it more often to keep it more in shape this way, but NEVER let it go drain it all the way!!!..it could not charge at all after...now here I come and say what is apple saying:

"For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Be sure to go through at least one charge cycle per month (charging the battery to 100% and then completely running it down)."

My question is, they are both running an li-ion battery, so why apple is taking this risk in doing an completely drain??? Are we at risk of not getting any charge after that? Are these batteries different? Are we not supposed to to maintain the battery main of the time in shape by charging it? Also there are some apps that will also makes an sound when the iPhone battery is 100% charged,is that mean that it can be overcharged?
Please keep your self thru the subject and show me your knowledge for this matter.

The llithium ion battery does not suffer from ""charging memory" issues of the older nickel based battery. That being said, I think it's important to understand that starting with a battery's manufacture at the factory, lithium ions oxidize in the battery, shortening its life. After a certain amount of time, the battery exhibits slightly different electronic properties, which the device can only detect when the battery is discharged. This type of problem is known as a "virtual memory effect" and occurs when your battery meter can show a high charge, then suddenly drop to low charge when the battery is almost dead. Rather than completely discharging the battery, I would suggest every thirty cumulative cycles, you should discharge lithium ion batteries until the phone gives a low battery warning, then recharge it. If you discharge lithium ion batteries to zero voltage, the internal safety circuit may open. In that case, a normal charger will be inadequate.

I hope this helps. Good thread by the way, I know a lot of people are confused by the proper method to charge/discharge the battery. :)