Well, ....note I said "rarely" and not "never". The reason preferred stock is rarely available to the public is because usually there aren't that many preferred shares available. Usually the people who have preferred shares never sell them, and if they do sell them, they are picked up very quickly.
Preferred shares CAN be bought by the public...if you can find them. lol
I don't know what Cramer was talking about...he must know this and to say "serious investors would buy preferred shares of sirius" is a little naive considering how hard it is to accomplish that statement.