Absolutely, yes. I have definitely bought games due to Youtube content (including but not limited to LPs). My three biggest examples would have to be Dark Souls, Binding of Isaac and Guild Wars 2. Both of the first were due to NorthernLion LPs, and the third was due to various Youtube guide videos, LPS and beta weekend previews.
Of course, yeah, there are also games I didn't buy after being interested in them and then searching them on Youtube. But that's often not because I got the full experience from an LP. Generally, it's because the LP or other content showed me that the game wasn't something that I would enjoy (or showed that the game was crap and not worth actually buying).
Of course, yeah, there are also games I didn't buy after being interested in them and then searching them on Youtube. But that's often not because I got the full experience from an LP. Generally, it's because the LP or other content showed me that the game wasn't something that I would enjoy (or showed that the game was crap and not worth actually buying).