So here is the reasoning behind this: Some of us are students with access to computer labs, others work for employers who have access to computers. Some of us visit customers. One thing that may become common among all of us is the restriction of installing software. However, it's not often the case where you can't plug in a USB stick. If it were possible to install the client and run it directly from a USB stick, it would make it more portable. It would also permit those, like myself, to play around with it on their lunch break or whatnot. I work for a large machine shop and I've got a computer at my workstation. I am not allowed to install anything on it, which I understand. However, I have internet access and pluggin in a USB stick is totally permitted.
It used to be a concern because the storage was limited on USB sticks. Now, $50 gets you a 128GB stick. That's nuts......