Nah I think you have a couple really good points, Isilde.
Firstly it is probably very different when you play, because the effects are actually important - they're conveying information to you. So I think it's pretty common when watching someone else play to be much more aware of the SFX as being obtrusive.
Speaking of the importance of good aural UI feedback, I'm always amazed how much WoW's subtle UI sounds add to that game - just pressing buttons feels right, because the sounds, visual ques, and your inputs are all so fluid and harmonious. I could do little more than sit in WoW and just mash keys, and it would still feel good - even if my character was feared or stunned or what have you.
In short, the UI feedback sounds add a tactile feeling to the game, and give it a sense of heft and solidity. Unfortunately if your fingers aren't doing anything, and you're just watching someone else play, even the best SFX can feel out of place. Furthermore, if they're just bloops and beeps it feels very digital and computer-y. Whereas, for example, WoW's UI SFX tend to sound like stone grating on stone, or metal sliding around, from what I recall.
Which leads into the second point you raise, which is a more subjective one: Some people really want those UI SFX to feel like they're part of the setting of the game. Others don't particularly care, or want the feedback to feel like they're on a computer, since they like the fact that they're on a computer playing a game. I'm in the latter group, as I'm less interested in total immersion, and perfectly happy to be made aware that I'm playing a game about a fantasy setting, rather than pretending I'm actually in one.
I think part of what's going on is that, if I can hazard a guess, you'd prefer any SFX feedback from the UI to feel like objects and tools from the GW2 setting were making the noises, whereas I, for example, just don't mind bloops and beeps, so they don't stick out to me.
Of course, I could be wrong. Either way it's a very interesting topic to think about from sort of a metagame/game design perspective.
Edited, Dec 10th 2010 11:20am by BriseBonBons