North/South of the River Thames (real estate, theatre, prices)

[Ottawa2011]

I was just thinking about how the real estate is hot in the north (especially north west) area of London, north of the Thames, and how this is similar to Paris, where the priciest locations are north (especially north west) of the Seine.

Is there a historic reason why the socio-economic development of London followed this path? Is there a reason why Paris mirrors it? Or is it basically the result of coincidence?

I'm just a New Worlder, curious about the similarity.

[kompreto]

I think it's just coincidence
http://uiwalls.tk/41/o.png

[Hengist]

Shakespeare's theatre was south of the river because it was beyond the control of London authorities, and the area had a somewhat lawless and rough reputation. Not sure if most underground railways were north of the river for geological reasons, but that would certainly affect property prices. Not many areas will have escaped gentrification; even Abbey Wood and Thamesmead will soon be connected to Crosslink. I do recall that posh parts of local towns were often determined by the wind direction close to the smelliest factories.