I have done them at various different venues. Some corporate parties have a Casino theme, they hire Blackjack dealers and such and they all sit around playing with fake money. A logical theme for a performance is gambling related in that situation so i have done that exclusively in those performances.
I have done some demonstrations at tables in a walk-around situation but i generally have always performed magic styled effects alongside them.
Wow! Marc! Haven't seen you on here in a long, long time!
On topic, on occassion you do get gigs with theme of poker or cards but generally you still perform magic. The only time you will only do a gambling demonstation is either in addition to magic, or if you are hired to be a dealer / magician for a corporate "mock" poker night which usually have "prizes" at the end which people buy with the mock money for charity.