An interesting one, and I suppose (to some greater, or lesser degree!) that it can be subject to a person's age, locality and individual personality/upbringing(?) - as to whether or not you start merely with a "request" and stop short of stating what that might be. The "rights & wrongs" are of course, another matter and no doubt should be in accordance with whatever enshrined publications and terminologies should be, in an ideal world.
I would suggest that usually any "request" made, is usually not of an urgent nature - and when hearing such calls made - usually the person making the "request", is waiting for a suitable quiet and unflustered point to make as such. Being human beings such as we are, I think in the main we all perhaps (even if subconsciously) like to be courteous, understanding and give the best chance to the receiver of our communications, time to 'prepare' themselves. I get that this isn't seen perhaps as the most exacting, most efficient way possibly in today's 'busy world/airspace' - but if there really isn't a vastly crowded frequency with huge and quick-fire swathes of exchanges occurring, does it really cause issues to have two possible exchanges? merely suggesting of course. I like to think of it sometimes akin to being with a friend perhaps, and already having established a dialogue - would you perhaps not say (assuming you have a request of them) - "Hey, Bob - mind if I ask you something?", as opposed to say "Hey, Bob - I'd like to go straight upstairs with your wife to the bedroom". Okay, every exchange has it's peccadilloes and the example is a little OTT I'll grant - but without overarching reason(s) as stated earlier in my reply here - Is it such a problem?.