Leaky? Like, other people can hear them?

I'd have a hard time caring about that if I had to wear headphones and play them loud enough to drown out the noise around me in the first place.

(Luckily, I have a door and a pair of headphones with a noise cancelling function that is usually good enough without even any music playing.)

That's what I mean. If you are in a work environment, you may want to isolate yourself from a discussion happening behind you, but that's not a heavy metal concert environment either, if you use the headphones sold along the iphone, everyone around you will hear your music.

But even in a very noisy environment, think the tube in London, where the noise level when going through a tunnel can be similar to a factory floor, surprisingly, people will hear your noisy iphone and will be annoyed by it. Now if it is in London they will be too polite to let you know. But I think not making annoying noise is also a form of politeness I like to adhere to in any case.

That doesn't make sense.

Why would you want to ADD to the problem instead of being part of the solution?