I mean one thing about "sneaking past to get the XP" is that if the monsters you avoided get drawn into a combat that gets noisy, then you don't get any XP for killing them. So sometimes you want to incapacitate the monsters when you could have snuck past them just because you don't want to fight both them and their buddies at the same time.
Again, bottom line, there's nothing in the rules that state the ONLY way to gain XP is by killing monsters. Its pretty easy to do however and a large focus of the PF system. If you like it, optimize for it. If you don't, don't. Play the game YOU want.You gain XP by defeating the encounter. Often this means killing the enemy, however it also includes talking your way past, charming your way past, and even sneaking your way past. If you faced the challenge and somehow got past it, then you defeated the challenge.
/cevah
Yup. The GM is in charge of encounter design and XP awards. It's within their purview to provide different--possibly larger--XP awards for finishing an encounter under conditions other than "you killed all the bad guys". That leaves a ton of design space for things other than damage maximization. For example, while defeating the enemies might constitute a CR 5 challenge, keeping the enemies at bay for ten rounds without killing them might be a CR 6 challenge, and doing so without significantly harming them at all might be even higher. There are all sorts of plotty reasons why such challenges might be pursued--maybe the enemies are possessed villagers and your ally is performing an exorcism ritual, and you might even need them to be conscious and lucid immediately afterward to militia up against the real baddies.
What if the solution is running away? Successfully mind you...
If you run away in a direction that means you must deal with them later, then no XP. If you run past them and get away, then you get the XP. Of course, if they follow and find you later, you don't get extra XP.
/cevah