This "don't let new users comment right away" idea is a frequent suggestion on HN, and one obvious problem with it is that some of the best threads on HN happen when the subject of a story posted here jumps into an HN thread for the first time to answer questions. Case in point: Nick Kokonas from Alinea Group has an account on HN ('nkokonas) because Tock, the restaurant booking company started out of Alinea, got mentioned here.

Delaying comments from new users would be of dubious benefit to the community (many of the worst comments on HN are not as a rule coming from fresh new accounts, and that safeguard is easily gamed), and what we'd lose in exchange is pretty clear. It hasn't been adopted here for a reason, not just out of laziness.