Yes, there is more risk in a preferred stock than in a bond.
First of all, the issuing company can suspend the dividend payment on a preferred and continue as an operating concern... without being in default. Also, most preferreds are non-cumulative, which means that the issuing company has no obligation to make up missed payments in the future.
Secondly, if a company is forced to reorgainze, preferred shareholders stand in line behind all of the debtholders (but in front of the common shareholders).
And finally, preferred shares typically have no maturity date, so there is considerable inflation risk associated with these securities. If inflation and interest rates go up significantly, the share price of your preferreds will decline, and you may be stuck with a low-interest-rate security in perpetuity.
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Now, with all of that said, I think there is a place for preferreds in a portfolio, but I don't consider them a "core" holding.
Also, you will see "trust preferreds" trading on the exchanges. These are backed by debt, so they are safer than an ordinary preferred issued by the same company. Since they're backed by debt, they do have a maturity date, although they are generally very long-term instruments.
Regards,
Duane