"because" has more the sense of cause and effect
"as" is used to indicate that something happens during the time when something else is taking place
Look at these sentences:
Because the sun was rising, Dracula returned to his coffin bed.
As the sun rose, I collapsed into bed after partying all night.
The very reason Dracula returns to his coffin is because he cannot live in the sunlight; whereas, the sun does not revolve around me!
Australian shares outlook - Higher as bargain hunters step in
Australian shares are expected to open higher Wednesday as bargain hunters step into the market, taking the opportunity to buy stocks at lower prices following yesterday's steep sell-off on renewed concerns about subprime mortgage related problems in the the global financial sector....
In your example: if 'because' had been used, then it would imply that the very reason stock prices were expected to open higher was as a direct result of bargain hunters buying. Yet the fuller report suggests that there was a dip in prices because of a major sell-off, so bargain-hunters jumped in before the expected upswing in prices again. Stock prices do vary. There are no grounds to suggest that the higher prices is a direct result of the bargain hunters buying. The two things are happening at the same time.
Be thankful for TV but not satisfied, as holiday season overwhelms audiences[/B]
Even more so with regard to the TV report: to use 'because' would suggest that 'you should be thankful for TV' because poor audiences are being overwhelmed by the holiday season. That is not what the fuller report is suggesting.
... I must say I'm thankful for TV's drama and comedy writers, who are conspicuous in their absence - or soon will be, as the writers strike leaves no new scripts to shoot. I've got an urgent Christmas wish: that the networks and studios stop playing Scrooge, and work out a deal that demonstrates they're as thankful for their writers as they should be.
As it was getting late, I decided to book into a hotel.
In this case, what is the difference between 'because' and 'as'? is there any nuance between them? What about the cases of 'while' and 'like'?
This one could go either way, depending on what the speaker/writer wanted to convey. Because it was getting late (and I don't like driving in the dark), I decided...
Using "as" has less of this feel of the whole reason for checking to book into the hotel was because it was getting dark. Let's rephrase it this way: As the sun slowly sank in the west, the weariness of driving all day was taking its toll, so I decided.." The two things - sun setting, and my deciding - just happen to occur at the same time: the real reason was because I was damn tired.
Because dark was setting in, we had to halt our search of this dangerous terrain till morning.