New users with reputation below 10 are allowed to post only 1 hyperlink in the response but they are allowed to add more than 1 hyperlink in the comment body.
Don't know if this was intentional, just wanted to bring to attention.
The limit for the number of links a user can add to a post serves to avoid spam.
Spammers are users using a not registered account, and with a reputation that is equal to 1. As such, they can just add a single link to their posts (as their reputation is lower than 10), and they can just comment for their own posts (as their reputation is lower than 50).
Spammers don't use comments for spamming; if they would do it (which is something I have never seen happen) there is a limit of 600 character for a comment, compared to the limit of 15K character for a post.
I guess the reason for allowing more links in comments is that abusing links in comments is less common than abusing links in questions/answers. (This probably also comes from the fact that commenting is limited for users with a reputation of 50+.)