i was born and brought up in dubai, grew up there and love it like my own country but like i said abu dhabi is a much better option for married couples for various reasons,some stated above. earlier even i used to think dubai was better but the traffic, lack of transport and ever rising charges on everything government related and other, makes life difficult in comparision to abu dhabi. the only attraction dubai has is the malls and other activity centres as well as theme parks which are equally accessible to anyone living in abu dhabi. living in abu dhabi u can avoid the traffic jams and other problems and yet enjoy the attractions of dubai.
maybe ur sister in law misses her husband too much!