Hi Surender..
when a cheque is crossed as A/c Payee then also the cheque can be ENDORSED to other person provided the endorsee has an account with some bank. This is the theory and as u said..there is a risk of forgery in this case..so,most of the banks do not prefer to collect a endorsed cheque even if it is a/c payee except in the case that the endorsor's account is also in the same bank . But theorotically, an a/c payee cheque also can be endorsed by mere writing the endorsee's name and signing on the back of the cheque.Only thing is that the payment cannot be made accross the counter but the amount is credited to the endorsee's account.
The case that u have mentioned was exactly the game plan of the famous Harshad mehta's forgery case.So, crossing of cheque only ensures the payment through bank account.