Comments are only available at 50 reputation points (or some number requiring a large number of previous reputation building actions), which a new user wouldn't have.
Are they? It's been long enough since I started that I'd forgotten. Still, 50 points is 5 upvotes, which is not difficult to attain quite quickly -- I earned >400 rep in my first two days with an account on Super User, and while that's not typical and took some effort on my part to achieve, a mere 50 points shouldn't be all that hard to manage by comparison.
