Nolaw:
Yes ofcourse its a scam. I am puzzled by why you think other than Rossi has come to the same result since Rossi wont tell how the device work (and ofcourse he has not filed any patents which you would normally do, provided it is not a scam).
Rossi said he would demonstrate the device worked, then he did nothing of the sort (essentially there are two ways to test the device; one is very complicated but allow cheating, the other is very simple and make cheating extremely hard. Ofcourse Rossi did not go for the later and at least one of the videos is highly indicative of cheating).
Secondly Rossi promised to ship the device a long time ago and ofcourse nothing of the sort has happened.
Finally this would not be the first scam Rossi has been involved in.
Do you want to bet 1000$ this device will conclusively be demonstrated to work within a year?