In most cases, yes. But not in all cases. The thing is, it is not normal to be able to make money on an empty property. So then, the expensive parts of London are not normal.
http://www.theguardian.com/society/2014/jan/31/inside-london...
http://www.standard.co.uk/news/london/lights-out-london-stre...
http://www.theguardian.com/uk-news/2015/jan/25/its-like-a-gh...
In the UK, the main political parities have resisted allowing a house construction boom for two main reasons. Much of middle England has got used to steep house price increases as normal income stream, so to slow it down is considered to be political suicide. And also much of the financial industry and upper classes are very used to it, so it would screw with the banks and the posh people to slow it down as well.
This means that currently London property is just guaranteed to rise (or so folk think), so it is considered an investment just to buy it and wait, and has been for at least 20 years.
This is also why they keep putting off raising interest rates. When they do it will get very messy.
Edit: HN doesn't let me write more comments. I still don't understand from those videos how they make money with the vacant houses. Also the articles are a bit weird, as if renting out a few houses in an expensive street would really have a significant impact on the housing issues of London.