Absolutely standard and shows the mortgage broker is doing a proper job (and note mortgage payment protection is completely different to single premium payment protection and is a valuable product to some people).
The problem they have is that the FCA and FOS, when dealing with a complaint against them, will ask to see the file detailing the sale of the mortgage and all associated products.
If the file does not support the mortgage broker's version of events they will find against them.
So, in this case, in x years time you get made redundant and your house is in danger of being repossessed. Someone mentions you could have taken out payment protection and you do not remember (or choose not to remember) whether your broker discussed this with you.
You complain and the FOS ask to see his file. He swears down he told you but there is nothing on file to support this, he is shafted.
By getting you to sign something it is clearly documented it was discussed with you and you do not want to take it.
I used to insure mortgage brokers against complaints and would very much expect to see this sort of thing on file.