...and someone has their headphones up loud I can hear mostly all the high end content of the music, but when im in my house and a boy racer comes within a mile radius in his car I only hear the 'thump thump thump' of the subwoofer low end and no high end content at all?

Frequency reproduction small ear buds = high , sub = low

With the car, you're also getting the, ahem, benefit of a largeish resonating chamber with room modes that happen to coincide with at least part of the bassline and the kick drum's output. In particularly poorly tricked-out Fiestas, you also get a nice little extra rattle every time that bass hits.

If you could hear any sub from a person with headphones he would have a BIIIIG head and very BIIIG headphones
If you could hear any high end from a car passing by the cabin was made of paper or it was an open car.

What happends when you place your hand in front of your loudspeakers tweeter ?

i kinda understand with headphones as they barely produce any bass at all... but with the car.. for example I used to live near a busy road, and i could be sitting in the back room and could hear only the faintest 'dum dum dum' as if the car was sitting at traffic lights miles away... Why is it that only deep bass energy can travel the larger distance?

The shorter the wave (higher frequency), the more quickly the wave's energy is transferred into the medium, dissipating the wave. The longer the wave (lower frequency), the farther the wave can travel before being damped out.

I'm not sure it's just a function of distance in the case of Mr Basshead sitting two blocks away in his XR2 - I used to be able to hear higher than just bass from open-air concerts on Clapham Common when I was living about a mile away up a hill. The difference in attenuation at 1km between 50 and 500Hz is only about 5dB IIRC, but it drops off quite quickly above that. But bass will travel much more readily through solid objects when higher frequencies will mostly bounce off them. You've also got less competition from everyday noise such as tyre hiss and engine rumble at the very low frequencies, so there's less masking going on with the low frequencies.