Some people like to play the game the complete opposite. Instead of 'wanting to be snuck up on', some people like to do the sneaking themselves. If every attack in the game was a surprise one, it wouldnt be very fun at all. Id constantly be getting snuck up on, and attacked.
The 'surprise' element is understandable however, but standing (or sneaking) next to a npc and not being able to identify them as hostile or non-hostiles makes no sense. So what do I just stand up and say "Hey! Are you a good guy or a bad guy? Because that is even less realistic than being able to 'sense' when there is a person or thing 5 feet away from you.
1) You will still be able to sneak without battle music or a radar. The only difference is that enemies that come rushing to you from some direction won't be as notable. And you wouldn't be able to sneak from them anyway. The attack would still happen.
Still, nothing stops you from using detect life. So to say that no battle music or no radar eliminates sneaking, is definitely not true.
2) What's more realistic...
to hear a battle music whenever an enemy notices you, despite you haven't noticed them yet, and to have a magical radar on your screen, as if you came from the 22th century...
or to just be a bit surprised from time to time with no notification that an enemy is rushing to you? The only notification you'd receive would be with your eyes (seeing the enemy), or with your hears (hearing the enemy's footsteps or w/e).
Also, what would be more realistic...
magically sensing who's bad and good and placing the bad as a red dot on a magical radar, as if you came from the 22th century...
or using your head and think a bit, depending on where you are (in a dungeon for instance) and how the supposedly enemy-character looks like, to find out whether he/she is an enemy or not?
I'm exaggerating a bit to say that thing from the 22th century, but it's kinda true at the same time. There is no radar in TES from what I know, and it shouldn't be that either.
You should plan your attacks by thinking,
not by looking mindlessly at some red dot at a magical radar or hearing some music-change.
If you aren't alert, then you won't be alert for nearby enemies. It's as simple as that, and that's how it should be like, imo.