How to play the commentary tracks?

[jens]

From another thread:
I think that it could be that Steam lacks the final data pack, it's out there on the Steam service, but it is probably still in "beta" so that is why you have not received your files for the commentaries. I have sent a mail to Steam, so hopefully they'll look into it as soon as they can.

Oh, so there is no misunderstanding, the missing data is only bonus content, so you can safely play the game without worrying about missing out on any of the regular game bits.