I understand why you require rep to comment on answers, but you must realize this discourages experienced engineers who have yet to create an account from participating on the site.
It's really not all that hard to get the 50 rep needed to comment anywhere.
Although I agree with your idea about experienced engineers not being able to comment, you must also understand that there are plenty of low-rep users that are not experienced engineers. Moderators like this policy because it keeps the little number in thier toolbar low - spammers are (often) in low-rep accounts.
Also, if experienced engineers really want to comment that bad, they can probably answer a question or two and get the needed reputation rather quickly. Spammers aren't known for their expertise in multithreaded iOS applications, and hence the rep barrier.