Bond ladderers take comfort in the fact that the bonds will be held to maturity; and, therefore, no matter what happens to yields, they can't lose money. This eliminates the fear that an active bond manager buys and sells at the wrong times. It is worth noting that parking funds in a money market fund is also a way to avoid the possibility of a loss.
How does all this compare to indexing? I'm glad you asked. Indexing is actually highly efficient. Bonds are replaced in the index essentially for free. A broad index like the Barclay's Aggregate Bond Index can be tracked with a low-fee exchange traded fund like AGG, which includes all investment grade bonds with a maturity greater than 1 year. Think about this. When bonds hit the 1-year mark, they leave the index. This is a time at which the yield on the bond is essentially a money market yield and, therefore, a good time to roll to a longer maturity in a steep yield curve environment. Professional bond managers use this 'riding the yield curve' strategy on an active basis. By doing so, they exploit the steepest part of the yield curve.
Furthermore, with the index you have a type of ladder going on. A certain portion of the portfolio is invested in each year--just like with a ladder. The big differences are that the index is marked to market and it is very well diversified. It would be interesting to see a study comparing performance of a laddered portfolio with a similar duration bond index.
According to Morningstar data, the lowest return of the Barclay's Bond Index over the past 10 years has been 2.43% (2005) and the highest return has been 10.26% (2002).