Besides, isn't it ultimately the Judge who determines the sentence, not the jury? Maybe it varies on the type of case and such but my point is the same.
Many places in the US require a jury to affirm a capital sentence.
I don't know what the deal is in full with that -- whether that's because it's considered Constitutionally-mandated, whether you need unanimous agreement, how common that is, etc. -- but the death penalty is a special case (and it's also the only case discussed here).
Adding features does not necessarily increase functionality -- it just makes the manuals thicker.