Not really rediculous. There are both technical constraints and financial ones.
Technical are that you are bouncind a full duplex signal set down the cable, the up and down stream carriers have to be suitably distinct and occupt different areas of the cable. If you want it symmetric you have to use 50% of the cable for each side, if you didn't have your 10:1 ratio, you would be complaining that your DSL was too slow
Financial constraints are that they need to have more expensive symmetric hardware on exchanges, and that the ISP's can load bandwidth onto the download connection which the vast majority use - and notice. Making more money from the same infrastructure.
Wont somebody PLEASEEEEEE think of the ISP's