i am currently using the above technique (one site for main content, the other as a blog with quick updates) and it's working well. but in the past in a similar situation i used to just have the two (actually more like 5 or 6) domains all pointing to the same site (i.e. i set up in godaddy that all my domains were pointing to the same DNS)

Can someone explain to me why the first technique is better than the second?

Cheers,
Chris