Witness`s signatures are not legally required. HOWEVER, with all the fraud that has surrounded mortgages and real estate the last few years, lenders are getting very sticky and are requiring those signatures.
I guess they want to know you, the signer, are who you say you are. But, if you plan to be fraudulent, why would a witness`s signature make it less fraudulent? Doesn`t make sense to me, but they set the rules.