I think it just depends on the individual crew.
Last time I flew with Virgin, the captain said:
"Virgin have some of the best cabin crew in the industry, sadly none are on board today - but they will do their best not to spill boiling coffee over you"
Everyone laughed, it got a great reception by the CC and SLF alike. The crew kept us well informed throughout the flight.
Yet coming back, we heard from the Flight Crew only on the ground in TAPA, then just prior to landing in EGKK. But perhaps he wanted to keep chatter to a minimum as it was a red-eye atlantic crossing.
I'm not sure about "rules", I think as long as its not unprofessional, its OK.