Why are bank stock P/Es so low?

[Vitaliy Katsenelson writes] In my piece on Lloyds TSB (NYSE: LYG), I wrote that banks usually trade at lower price-to-earnings ratios to the market, because they are considered riskier investments as a result of their high use of debt. That line caught the eye of Foolish financial editor Joey Khattab, who asked writers Stephen Simpson and Nate Parmelee whether they agreed with my logic. Both disagreed. They argued that larger banks generally have lower P/Es because they are perceived to have a slower or more limited growth potential.

At first, I thought there might be a conspiracy of Fools at work against me! So I asked several investment professionals for their opinion. And to my amazement, they all agreed with the Fools.