TimeofMind, you can absolutely use the standard Bitcoin client. There are problems with that though for a lot of people, although it may not be a problem for you.

One disadvantage of using the Bitcoin client to store your BTCs is that you have to spend them from the same device the client is being run on, or another device that is running the client. The Bank of Bitcoin makes it where you can spend your BTCs from any internet-connected device, anywhere in the world. That device does not need to be running the standard client. You could pick up your friend's iphone and spend your BTCs from there. Being able to pay someone in BTCs from your cell phone is a convenience that not many people have right now (or unfortunately need, but we're hoping to help change that). You could receive BTCs on your cell, and spend them from your work computer without any special software.

Running the client is also a huge drain on memory and bandwidth, which may not be a problem for you but is a problem for many people- and is a barrier in terms of BTC being adopted by the world. Running Bitcoin software on your own computer or other device typically requires downloading the full Bitcoin "block chain". The block chain is the full history of all Bitcoin transactions which have occured since the inception of Bitcoin. This is currently about 7GB of data and growing quickly. Maintaining a full copy of the block chain requires an ever-increasing allocation of memory, and the constant downloading of new transactions makes it impractical (and essentially impossible for people with slower Internet connections).

Our solution is to download and store the block chain on our server. We use our memory and bandwith, thus freeing up your resources, making Bitcoin easily accessible to all. This is in large part an effort to make this a more convenient (and therefore viable) currency. Thanks.