Granted, any legitimate business shouldn't block their number but, again, what would you do if you missed an important call because they blocked these types of calls.
I disagree, it is not uncommon for legitimate businesses to block their number. For example, doctors routinely make phone calls from blocked numbers so that they do not get return calls which do not go through their switchboards. Same goes for lawyers, etc...
My doctor explicitly informs his patients to allow blocked numbers if you want calls from his office. They will not unblock their number if your home line does not accept blocked numbers and you will not get calls with information about appointments, lab results, etc...
Lawyers don't always work with the most respectable people around and routinely block their number even when making calls to clients, unless they are a favored client. A lawyer does not want their clients calling their cell/home phone at all hours of the day/night.
Of course, these types of businesses would leave a message requesting a callback if needed.
I certainly don't want unknown numbers blocked from my phone for this exact reason.