An average web developer in no way can compare to a lawyer or a doctor.

First of all, doctors generally save lives. And they have to go to school for at least 8 years. Lawyers, almost just as long.

How long does it take to learn Rails, HTML, and Javascript? A few months?

Average web developers are not that special. However, great engineers for whom Rails is an afterthought compared to what they know, are indeed comparable.