At a guess, where no radix is specified in the listing, it makes it easy to spot which type is being used at a glance, but also makes it perfectly clear to the compiler.
Binary is pretty easy to spot and hex is also easy to spot when A to F are used, but without anything to provide clarification there can be some confusion.
IIRC, MPASM assumes you are using hex until you specify otherwise.
Consider the use of 10 as a value.
Without any specific information as to the correct radix used, MPASM sees it as 10 in hex, which is 16 in decimal. If you actually meant 10 in decimal.....
Sometimes, programmers will list the radix used at the top of a listing.... "list r=dec" or "radix dec" "radix hex" or something else.... other times they will not and that is where the 'extra' info helps.
I'm quite sure that others will add to this and also correct any errors I may have made, but I hope this helps you.
EDIT: Other posts were made whilst composing this...