your spinal cord controls the majority of walking, leaving your brain free to do other things such as chew gum, talk, or listen to cheesy overdubbed nickelback songs.
the reason why the songs sound the same is they ARE algorithmically equivalent. the verses, choruses, pickups, and bridges are EXACTLY the same length; as well as harmonically, rhythmically, and melodically congruent. there is _minimum_ artistic/creative variation between them... they both clearly came from the same formula. this band should be embarassed; that is not music.
one might also argue the reason the songs fit together is they are in the same key; they'll naturally go together, right? wrong. its more than possible to create harmonic dissonance by playing two seperate progressions simultaneously in the same key.
i think if one were to listen to stairway to heaven in one ear and welcome to the jungle in the other, youd most likely be aware that you are in fact listening to two seperate songs. nobody stands between two stages at a music festival and is tricked into thinking theyre hearing one song.
mts: i don't deny by any means that you could be right (to some degree), but i think you are taking the concept a bit out of context.