The Shepherd book is clear that gambling is a potential DF offence but seems to differentiate between repeated participation in gambling for personal greed (e.g. online, betting shops, racing etc. etc.) and small games for low stakes that might happen in families or as a casual thing amongst friends.
Some famillies may have occassional games where very low value coins are used and it seems that whilst the WT article tries to imply these are not acceptable, the Shepherd book tells the elders to avoid getting involved in judging people on this when you are talking about very low level gambling for "entertainment".
My thinking is where does the line get drawn? For example, if a Witness bought a lottery ticket on occassion, engaged in low level online poker, had a punt on the Grand National (the one race in the UK everyone has a pop on, often as part of a sweepstake at work), popped a couple ofquid into a slot machine in the pub on a Friday night etc. then could they argue it was purely for entertainment and the elders should butt out?
It seems to me a bit like the porn thing - if you know the hidden rules then you can get away with stuff that most ill-informed Witnesses would automatically assume was a no no.