Switching to a browser on my pc required me to exit Fallout 3 (probably will be same case for Vegas) so going The Vault website was a pain when I was playing hence this is why I'm actually considering purchasing the guide (I don't care about any minor inaccuracies lol)
This is about the only reason to buy a guide. However I have a couple of laptops that I can use while gaming to look up things on line as I play.
I do think guides are nice to have for some games, even if the information is on line. Then again, I pay for and read Wired Magazine in magazine form even though I can get all the content for free on line. Sometimes I just prefer the printed word on paper than text on a screen.
Personally, I would get the Collectors Edition as in that case, the guide, which is in a nicer format in CE, is practically free with purchase when you buy the CE game.