Why would you question all the realtors?
Have you purchased 500 homes in the past few years?
Well I'm sure the professional realtors giving you this good advice have been involved in this many deals!
It has almost become rude and inconsiderate for any buyer needing a loan to close on a deal in 2012 to ask to even look at homes without doing something so easy and basic as taking time to get pre qualified to obtain a letter.
As a Mortgage Broker I ADVISE YOU TO DO AS YOUR REALTOR REQUESTS YOU DO
If you were a seller, I would tell to you that NOBODY gains access to your home without a letter..PERIOD!