I noticed the same clause in the TOS last week and was taken aback. Ideally I'd love to be able to distribute my Google+ URL with the same confidence as I distribute my email address: namely,
if you send a message to this address, you can guarantee that I'm the one who receives it. The fear here is that, should Google start charging for this "service" in the future, and should I decline to play along, someone else could squat on my former URL and intercept any traffic intended for my page. Please, Google, for my own peace of mind, either make this a paid service
up-front, or pledge that a given URL will always alias to the same individual.
(Though perhaps the email analogy is a bad one, since IIRC both Yahoo and MSN periodically release long-dormant addresses back into the eligible pool. Though still unsettling, it's a more reasonable approach than "we may force you to start paying us an unknown amount at some unknown future date".)
Ultimately, I was about to go through with it anyway until I realized that doing so would require me to register a phone number with my Google account, which I have so far avoided. That requirement was the final straw.