Once you get to a stage where your client is using 15gb bandwidth a week it defeats the purpose of having a p2p currency when you will be forced to use an online wallet which means your coins can be traced.
Donate to wikileaks from blockchain.info and receive a drone attack through your window

Believe it or not some places have bandwidth caps and you can be shut out of the network if you value controlling your own wallet.
If bitcoin gets to this stage anyone who values financial privacy will not use it. So its good to have alternatives because using a thin client that relies on someone elses server isnt the answer.