ADSL SPEED

Well i am little confused with this speed thingi,,

ADSL speed of 1MB, gives 1024 download and 640 upload,,
ADSL speed of 2MB, gives 2048 download and 640 upload,,

Q1> why isnt upload equal to the download.
Q2> why isnt the upload doubling in 2MB

I just dont get this thing why is there this difference,

The 'A' in ADSL stands for asymetric. The product is designed for internet access where you typically download far more than you upload. Therefore they sell it based on the download bandwidth you get. The upload bandwidth does increase with the download bandwidth, but only to keep your connection from slowing down too much