Although you're of course correct that people have always followed this pattern, I think you're missing the fact that there have been genuine shifts in the London property market that are driving this trend to an unusual extreme.
The proportion of foreign buyers of London property has nearly doubled, from 23% in 2005 to 38% in 2012 according to Savilles & I'd guess that it's going to be higher this year. Many of those buyers are looking not for income but simply for places to park capital so they don't rent out the properties which remain empty (this is especially true of Chinese buyers, apparently for cultural reasons). Consequently those people who are living in London (or would like to) are competing over a smaller pool of properties. The net effect on rents and house prices is exactly what you'd expect: both are going up sharply.
Yeah. Last I heard, there were new-build tower blocks full of apartments that sold out rapidly but have remained almost entirely unoccupied because they were bought by foreigners as a safe way of storing their wealth.
(Normally this would cause problems with squatters but the government changed the law to make it a criminal offense to squat in empty buildings and allow the police to forcibly remove them. They were helped with this by a sob story in the Daily Mail about someone who'd gone on holiday and found his house full of squatters; what the Daily Mail didn't mention is that it was a buy to let property and he didn't actually live there.)
The proportion of foreign buyers of London property has nearly doubled, from 23% in 2005 to 38% in 2012 according to Savilles & I'd guess that it's going to be higher this year. Many of those buyers are looking not for income but simply for places to park capital so they don't rent out the properties which remain empty (this is especially true of Chinese buyers, apparently for cultural reasons). Consequently those people who are living in London (or would like to) are competing over a smaller pool of properties. The net effect on rents and house prices is exactly what you'd expect: both are going up sharply.