[Calling him a scammer isn't warranted as he's done nothing of the sort though I am abit suspicious or sceptical of him though maybe I'm being overly cycnical. If he asks for a big ammount for something in the future then I'd advise caution but I think it would have to be quite big amount if he was trying to scam just to recoup all the money from his other giveaways. I guess only time will tell me I'm not expecting him to pull off a scam but at the same time wouldnt be surprised either.
You're right on that. For as far as I know he has not scammed anyone yet. Some might accuse him of "Buying trust", but I don't agree on that. See
THIS post of Quickseller and see how much money he (Bob) gave away in just a short time.. There has not been such thing as a scam to cover all these cost has it?
I think Bob is just a great, generous guy. I've once received an incredible cheap code for Steam money of him, and next to that I've received a (LEGIT!!) digital Amazon code of him for only making a $2 donation to charity. Read, this code was legit (and it still is: the balance has not been deducted in my Amazon account where it still is located).
The reason why someone would be so generous to strangers, keeps unrevealed I guess. Personally I think he was one of the lucky ones who joined the Bitcoin train in the very beginning (and therefore has or had a lot of BTC / money).
You should notice that he especially helps people who have shown to be great persons too, for example
Muhammed Zakir.